Been working on fintech API integration projects lately — connecting banking cores, payment processors (Stripe/Plaid-style), and KYC/AML services into a single backend — and wanted to compare notes with others who’ve done this.

A few things that have been non-obvious in practice:

• Webhook reliability varies a lot between providers — some (like Plaid) are solid, others need heavy retry/dedupe logic on our end
• Rate limits differ wildly depending on whether you’re in sandbox vs. production, which trips up staging environments
• Error handling for partial failures (e.g., KYC passes but bank-link fails) needs its own state machine, not just try/catch

At work we’ve run into most of these across a few client integrations, curious if others have found better patterns — especially around handling provider-specific webhook quirks without ending up with a pile of provider-specific if/else branches.