Blackcurrant Finance: Accounting & Open Banking Platform
Live bank transaction import via PSD2 AISP flow with Barclays Open Banking API
Background
Blackcurrant Finance wanted to reduce the manual bank reconciliation burden for SME accountants by pulling live transaction data directly from UK banks via Open Banking, and to enable payment initiation from within the accounting workflow. Accountants managing multiple SME clients were spending real hours every week downloading bank statements and matching them line by line against the ledger, a task that scales linearly with client count and leaves plenty of room for mismatched or duplicated entries.
What We Built
A microservices platform with three core apps: an accounting service, a payments app, and an Open Banking integration app. Services communicate via RabbitMQ so a slowdown in one concern (say, a bank API being flaky) never blocks the others. Angular frontends serve the client-facing accounting UI and payment management views. The Open Banking integration handles PSD2 AISP (account information, transaction import) and PISP (payment initiation) flows with Barclays. eIDAS certificates were provisioned for PSD2-compliant API authentication, the regulatory credential UK banks require before they'll hand over live account data.
Architecture
- Accounting service
- NestJS microservice, core ledger and reconciliation logic
- Payments app
- payment processing and status tracking
- Open Banking app
- AISP/PISP flows, bank consent management, transaction normalisation
- Event bus
- RabbitMQ for async inter-service messaging
- Auth
- JWT with role-based access; eIDAS certs for bank API auth
Results
Bank statements reconciled by hand, one SME client at a time
Transactions imported live via PSD2 AISP and matched automatically
Payments handled in a separate system from the accounting workflow
Payment initiation built directly into the platform accountants already use
Outcomes & Lessons Learned
- Live bank transaction import via PSD2 AISP flow with Barclays Open Banking API
- Payment initiation (PISP) enabling outbound payments directly from the accounting platform
- Microservice architecture with RabbitMQ decoupling accounting, payments, and Open Banking concerns
- eIDAS certificate management for PSD2-compliant API authentication
PSD2 certificate management (eIDAS provisioning, renewal, and secure storage) proved more operationally intensive than the integration code itself. Building a dedicated certificate rotation workflow at the outset would have saved significant time later, since a lapsed certificate silently breaks every bank connection at once.
Questions, answered.
The things people ask us about this project. If yours isn't here, ask us directly, we reply like humans.
Ask us anything→How does live bank transaction import work?
Through a PSD2 AISP (Account Information Service Provider) integration with Barclays Open Banking, importing transactions directly rather than requiring accountants to download and reconcile bank statements by hand.
Can payments be initiated from within the accounting platform?
Yes, a dedicated payments app handles PISP (Payment Initiation Service Provider) flows, so outbound payments happen from the same platform accountants already use for the ledger.
Why split this into separate microservices instead of one application?
So a slowdown or failure in one concern, like a flaky bank API, never blocks the others. The accounting service, payments app, and Open Banking integration communicate via RabbitMQ rather than being tightly coupled.
What's involved in authenticating with UK banks under PSD2?
eIDAS certificates, the regulatory credential UK banks require before releasing live account data, which we provisioned and manage as part of the integration.
What was the most operationally demanding part of maintaining this?
PSD2 certificate management, provisioning, renewal, and secure storage of eIDAS certificates, proved more demanding than the integration code itself, since a lapsed certificate silently breaks every bank connection at once.
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