API security compliance becomes harder when fintech teams connect payment products to third-party providers, banks, account information services, payment initiation services, or open banking platforms.
A TPP integration can change the risk profile of an API quickly. What once looked like a clean internal service may become part of a wider payment data and transaction ecosystem. It may exchange tokens, expose account information, initiate payments, manage consent, route payment requests, or connect to systems that influence PCI-related environments.
Open banking payments can reduce card use in some flows, but they do not remove security responsibility. For fintech teams, the question is not only whether card data moves through the API. The question is whether the API can affect payment data, payment authorization, payment initiation, customer consent, transaction records, or systems connected to PCI compliance.
TPP Integrations Turn APIs Into Payment Risk Points
A third-party provider integration can turn an API into a payment risk point because it expands the number of parties, tokens, permissions, endpoints, and workflows involved in a transaction.
Fintech API security becomes more complex when an application connects to TPPs, banks, payment initiation service providers, account information service providers, open banking gateways, data aggregators, fraud tools, identity services, or payment orchestration layers. Each connection can create a new trust relationship. Each trust relationship needs authentication, authorization, consent validation, logging, monitoring, and evidence.
The risk is not limited to the external provider. The fintech’s own API may become the layer that accepts customer instructions, stores consent references, exchanges access tokens, initiates payment requests, retrieves payment status, or sends account-to-account payment events into internal systems. If that API is poorly governed, the TPP integration can become an entry point into payment workflows.
PCI compliance for fintech teams depends on understanding where the API sits in the payment environment. PCI SSC explains that PCI DSS provides a baseline of technical and operational requirements designed to protect payment account data through its PCI DSS standard. If a fintech API stores, processes, transmits, or can affect the security of payment account data, the API cannot be treated as a simple integration layer.
A TPP integration should therefore trigger a fresh scope review. Teams should ask what data moves through the API, which systems it connects to, what tokens it stores, what payment actions it can trigger, which logs it produces, and whether it touches cardholder data environments or systems that support them.
An API connected to payment workflows is not just software plumbing. It is part of the payment risk surface.
Open Banking APIs Reduce Card Use but Not Compliance Risk
Open banking payments and account-to-account payments can reduce dependency on card rails, but they do not eliminate compliance risk.
In an A2A payment flow, the customer may authorize a payment from a bank account rather than entering card details into a checkout form. That can reduce exposure to card data in some designs. But the fintech still has to secure the API endpoints, customer journey, consent records, payment initiation events, authentication flows, logs, status callbacks, error handling, and integrations with banks or TPP platforms.
Open banking API security also depends on the structure of the market and the payment model. In the UK Open Banking Standard, for example, the Payment Initiation API Profile describes functionality for registering a payment-order consent, submitting the payment order for processing, and retrieving payment-order status. Those functions are operationally sensitive because they influence whether a payment is staged, authorized, and tracked correctly.
The compliance risk also depends on what happens around the open banking flow. A fintech may combine open banking payments with card payments, wallets, subscriptions, customer accounts, fraud tools, reconciliation systems, or merchant dashboards. If the API connects open banking flows to card-related systems, PCI cloud environments, payment gateways, or transaction databases, the PCI review may become more complex.
Open banking can change the payment rail. It does not remove the need for payment API compliance.
Fintech teams should avoid a narrow assumption: “No card entered here, so no payment security concern exists.” That assumption ignores API authorization, consent integrity, fraud risk, transaction manipulation, data exposure, and connected payment infrastructure.
Customer Consent Controls What the TPP Can Access
Consent is one of the most important controls in open banking API security.
A TPP should not receive broad access simply because the customer approved one payment or one account connection. Consent should define what the provider can access, what action it can perform, which account is involved, what payment permissions exist, how long access lasts, and how the customer can revoke or change that consent.
Open Banking Limited explains that Payment Initiation Services enable a PISP to initiate a payment order with the payment service user’s explicit consent from an online payment account held at the account-servicing provider. That explicit consent model is central to payment initiation because the customer is authorizing a defined action, not giving unlimited access to financial activity.
Consent becomes risky when it is too broad, poorly recorded, weakly enforced, or hard to revoke. A payment initiation API should not let a TPP reuse old consent for a different amount, different payee, different account, or different payment purpose unless the flow and governing rules allow it. An account information integration should not expose more account or transaction data than the customer authorized and the product requires.
Token-based access makes this even more important. A fintech may store consent IDs, authorization codes, access tokens, refresh tokens, scopes, and account permissions. If those values are mishandled, a TPP or attacker may gain more access than intended.
Good consent governance should connect the customer approval event to the technical permission granted through the API. The business should be able to prove what the customer approved, when it was approved, what the TPP received, how long the permission remained active, and how revocation was handled.
Consent is not only a user-experience step. It is an access-control boundary.
Broken Object Authorization Can Expose Account Data at Scale
Broken Object Level Authorization can turn one API flaw into large-scale payment data exposure.
BOLA happens when an API does not properly verify whether the requester is authorized to access the specific object being requested. In fintech, that object might be a customer account, payment consent, transaction record, refund record, payment initiation request, merchant profile, bank connection, statement, token reference, or payment status resource.
OWASP ranks Broken Object Level Authorization as API1 in the OWASP API Security Top 10 2023 and explains that attackers can exploit vulnerable endpoints by manipulating object identifiers in requests. In an open banking or payment API, that could mean changing an account ID, consent ID, payment ID, merchant ID, or transaction reference to access another customer’s resource.
BOLA API security is especially important because APIs often expose structured identifiers. A fintech may use UUIDs, database IDs, resource references, account numbers, consent IDs, or payment-order IDs across endpoints. Even if identifiers look hard to guess, the API still needs object-level authorization checks. The system must confirm that the authenticated user, app, or TPP is allowed to access that exact resource.
This risk becomes more serious in TPP integration because multiple parties may operate across the same API surface. A TPP may act on behalf of a customer. A merchant may access payment reports. A support user may view transaction events. A bank connection may send status updates. Each role needs precise authorization.
Authentication answers who the requester is. Authorization answers what that requester can access. BOLA appears when the second answer is missing or incomplete.
Weak OAuth and Long-Lived Tokens Create TPP Entry Points
OAuth security is central to open banking payments because tokens often control access between customers, fintech platforms, TPPs, and banks.
A weak OAuth implementation can create serious API security compliance risk. Problems may include poor client validation, insecure redirect handling, weak token storage, excessive scopes, long-lived access tokens, refresh-token abuse, missing MFA, weak session controls, token replay, inadequate revocation, and failure to bind tokens to the correct client or consent context.
Open banking environments often use hardened OAuth profiles because ordinary OAuth configuration can be risky in high-value financial use cases. The OpenID Foundation’s FAPI 2.0 Security Profile describes a security profile suitable for high-security applications based on the OAuth 2.0 Authorization Framework. This matters for fintech API security because payment initiation, account data access, and customer consent flows require stronger assumptions than a low-risk login integration.
Long-lived tokens deserve special attention. If an access token remains valid for too long, an attacker has more time to use it. If refresh tokens are not protected, rotated, monitored, or revoked properly, a compromised integration can regain access even after the initial access token expires. If token scopes are too broad, one compromise may expose more account or payment functionality than needed.
API token security should also include revocation and expiry evidence. Teams should know which tokens exist, which consent they map to, which TPP or client they belong to, when they expire, when they were last used, and whether suspicious token activity occurred.
In a payment API, tokens are not just technical artifacts. They are delegated access to financial actions and data.
Payment APIs Need Strong Customer Authentication Evidence
Payment initiation APIs need evidence that customers were properly authenticated and that payment actions were properly authorized.
Strong customer authentication requirements vary by jurisdiction and payment model, but the operating principle is useful for fintech teams everywhere: payment actions need clear proof of who authorized them, what they authorized, and whether the authentication and consent records match the payment event.
Where PSD2-style requirements apply, strong customer authentication and dynamic linking become especially important. The European Banking Authority has explained through its Q&A material that when SCA is applied for certain electronic payment transactions, the payer should be made aware of the amount and payee, and dynamic linking requirements connect authentication to transaction data. That principle reduces the risk that a customer authenticates one action while a different payment is initiated.
For fintech teams, SCA evidence may include authentication logs, consent records, authorization timestamps, payment initiation requests, payee and amount data, device or session information, approval events, challenge outcomes, revocation records, and status responses from banks or open banking providers.
This evidence matters during disputes, fraud investigations, regulatory review, internal audits, and payment API compliance assessments. A fintech should be able to show that payment initiation cannot be abused through replay attempts, consent substitution, token misuse, unauthorized payee changes, or invisible transaction manipulation.
Customer authentication is not only a front-end event. It must connect to the API record that proves the payment action was legitimate.
API Inventory Decides What Falls Into PCI Review
Fintech teams cannot manage payment API compliance without knowing which APIs exist.
A TPP integration may introduce public APIs, internal APIs, partner APIs, open banking APIs, payment initiation APIs, consent APIs, callback endpoints, reporting APIs, authentication endpoints, and third-party components that support the payment journey. Some may be actively maintained. Others may be shadow APIs created outside the official release process or zombie APIs left behind after a product, version, or partner flow was replaced.
An API inventory should show each endpoint’s purpose, owner, environment, authentication method, authorization model, data classification, connected endpoint’s purpose, owner, environment, authentication method, authorization model, data classification, connected systems, token use, payment function, logging coverage, and whether it touches or affects PCI-related systems. Without that inventory, teams may miss endpoints that expose payment data, support account-to-account payments, influence customer consent, or connect to PCI-relevant environments.
OWASP’s API9:2023 Improper Inventory Management highlights why API visibility matters: APIs often expose more endpoints than traditional web applications, making documentation and inventory critical. For fintech teams, that means API inventory is not a documentation exercise. It is a scope-control mechanism.
A fintech may believe its PCI scope is narrow because card data is not directly entered through an open banking flow. But if an API connects open banking payments to card-related systems, transaction databases, merchant dashboards, reconciliation tools, fraud engines, or payment orchestration platforms, the review may become broader.
You cannot protect an API you do not know exists. You also cannot exclude it from PCI review safely without understanding what it does.
Public-Facing APIs Need Protection Before Attacks Reach Them
Public-facing API security should begin before attackers reach the payment workflow.
Open banking and fintech APIs are attractive because they connect identity, consent, money movement, account information, transaction records, merchant systems, and payment initiation logic. Attackers do not always need to break encryption or steal card data directly. They may abuse weak authorization, excessive data exposure, replay behavior, rate limits, predictable identifiers, weak token handling, or unprotected endpoints.
Runtime API protection should include authentication enforcement, authorization checks, rate limiting, schema validation, anomaly detection, abuse prevention, API gateway controls, logging, monitoring, and alerting. The goal is to detect suspicious calls before they affect customer accounts, payment initiation, consent records, or transaction workflows.
OWASP’s API Security Project is useful for fintech teams because it focuses on API-specific risks such as broken authorization, excessive data exposure, unrestricted resource consumption, and improper inventory management. Those risks map closely to open banking API security because fintech APIs often expose structured resources and high-value actions through predictable workflows.
Public-facing API controls should also distinguish normal customer behavior from suspicious automation. A payment initiation API may receive legitimate retries, status checks, or bank callback events. But repeated consent attempts, unusual token use, excessive failed authorization, manipulated object IDs, unexpected geographic patterns, or abnormal request volume may indicate abuse.
API protection should not sit only at the network edge. It should understand the payment workflow behind the endpoint.
API Testing Must Cover Business Logic, Not Just Endpoints
API testing must go beyond basic vulnerability scanning.
A scanner may find missing headers, outdated software, injection risk, or exposed endpoints. Those checks are useful, but open banking payment APIs also need testing for business logic abuse. A payment initiation API may be technically available, authenticated, and encrypted while still allowing the wrong action at the wrong time.
Business logic testing should examine broken authorization, consent bypass, payment initiation abuse, replay attempts, transaction manipulation, excessive data exposure, weak rate limits, stale tokens, account switching, merchant impersonation, and status manipulation. It should also test whether a TPP can access only the customers, accounts, consents, and payment resources it is authorized to use.
OWASP’s API Security Top 10 2023 is a strong reference point because it highlights API risks that ordinary web testing can miss. For fintech teams, the most important lesson is that APIs fail through workflow assumptions as much as through technical vulnerabilities.
Testing should follow the real payment journey. Can a customer approve one payment while the API submits another? Can a consent ID be reused outside its intended scope? Can a TPP retrieve a different user’s transaction record by changing an object reference? Can an expired token still be used? Can a payment status callback be spoofed? Can a deprecated endpoint still expose sensitive data?
Payment API testing should prove that the business rule is enforced, not only that the endpoint responds.
Training Helps Fintech Teams Control TPP API Scope
TPP integration risk often sits between product, engineering, compliance, security, and payments teams.
Product teams may design the open banking journey. Engineers may build the API. Security may test authentication and authorization. Compliance may review PCI scope and regulatory evidence. Payments teams may manage settlement, reconciliation, and payment initiation flows. Partner teams may manage third-party provider integration. If those teams do not share the same API risk model, hidden compliance gaps appear.
Teams working through Open Banking Payments And PCI Compliance For Fintech Teams can build practical understanding of API security compliance, open banking API security, TPP integration, OAuth security, API token security, BOLA API security, strong customer authentication evidence, API inventory, public-facing API security, and payment API compliance. This training is useful because fintech API risk is not owned by one function alone.
Training should help teams ask the right questions before a TPP integration goes live. Which APIs are exposed? Which endpoints initiate payments? Which tokens are long-lived? Which consents are active? Which logs prove SCA? Which APIs connect to PCI-related environments? Which shadow or zombie APIs still exist? Which tests prove that authorization works at object level?
A fintech API should not become a compliance surprise after launch. The scope should be understood before customers and TPPs begin using it.
Conclusion
A TPP integration can bring PCI and payment security risk into the API layer.
Open banking payments and account-to-account payments may reduce direct card entry in some flows, but they do not remove API security compliance responsibilities. Fintech teams still need to secure authentication, authorization, consent, tokens, payment initiation, transaction records, logs, partner access, and connected payment systems.
The API becomes part of a wider payment ecosystem. If broken object authorization exposes account data, if OAuth tokens last too long, if consent is too broad, if SCA evidence is weak, if public endpoints are unprotected, or if shadow APIs remain active, the fintech may create hidden payment risk even without a traditional card checkout form.
Strong API security compliance depends on visibility, authorization, evidence, runtime protection, and testing. Teams need a complete API inventory, strong OAuth governance, clear consent records, object-level authorization checks, public-facing API protection, business logic testing, and PCI scope review for connected systems.
TPP integrations can create value. They can also create payment risk if the API is treated as a technical connector instead of a compliance boundary.
FAQs
What Is API Security Compliance?
API security compliance is the process of securing APIs according to security, payment, privacy, regulatory, and internal control requirements, including authentication, authorization, logging, testing, and evidence.
How Can a TPP Integration Affect PCI Compliance?
A TPP integration can affect PCI compliance when APIs connect to payment systems, cardholder data environments, payment records, transaction systems, or infrastructure that influences payment security.
Do Open Banking Payments Remove PCI Risk?
Open banking payments may reduce direct card use in some flows, but they do not remove API security, consent, authentication, authorization, logging, or connected payment-system responsibilities.
Why Is API Inventory Important for Fintech Compliance?
API inventory helps fintech teams identify public, internal, partner, payment, open banking, shadow, zombie, and deprecated APIs that may expose payment data or affect compliance scope.
What Is BOLA in API Security?
Broken Object Level Authorization is an API flaw where a user, app, or TPP can access another customer’s resource by changing object identifiers without proper authorization checks.
Why Are Long-Lived Tokens Risky?
Long-lived tokens increase risk because a stolen or misused token may remain valid long enough to access data, reuse consent, initiate activity, or maintain unauthorized access.
What Evidence Supports Strong Customer Authentication?
SCA evidence may include authentication logs, consent records, approval events, transaction details, payee and amount data, device/session records, and payment initiation records.
What Are Shadow APIs and Zombie APIs?
Shadow APIs are undocumented or unofficial APIs. Zombie APIs are old or deprecated APIs that remain accessible after they should have been retired.
Why Must API Testing Cover Business Logic?
Business logic testing checks whether payment workflows can be abused through consent bypass, authorization flaws, replay attempts, transaction manipulation, or excessive access.
Who Needs PCI API Compliance Training?
Fintech product, engineering, security, compliance, payments, partner, and operations teams all need training because TPP API risk crosses technical and business functions.
