bKash and Nagad in your checkout: what integration really means

Most "payment integration" conversations stop at the API redirect, which is a weekend of work. The real project starts after the redirect — in callbacks, ledger states and the monthly moment someone asks where the money actually is. Here is the honest shape of accepting mobile financial services (MFS) on a Bangladeshi product, written as a map rather than a pitch.

The flow, with the parts vendors skip

• Checkout opens an intention: your server asks the gateway (direct MFS APIs are typically reached through licensed aggregators) for a token, then the customer approves in the wallet app or via OTP on their phone.
• The callback is a suggestion, not a verdict. Payment is confirmed when your server verifies the transaction state against the gateway — on a bad network, callbacks arrive twice, late or out of order. Your system must be idempotent: one order, one money state, no matter how many times the phone rang.
• The ledger is the truth. Every confirmed payment is a row only your system owns: amount, wallet reference, timestamp, state. If a customer disputes a charge, the answer is the ledger — not a gateway dashboard screenshot from three weeks ago.
• Refunds go back the way they came, and that is a state machine too: requested, sent, confirmed, failed. "We will refund you over the phone" is how support teams lose arguments.

Reconciliation: the feature nobody demos

Every settlement cycle, the gateway's report and your ledger must agree line by line. They will not always — timeouts, partial failures and human error exist. The integration that matters can answer, without a spreadsheet: which orders were paid but never captured, which captures have no order, what changed since last night. We build this as an end-of-day check that produces a difference number; zero is a state you arrive at, not a hope you type in.

What is on the other side of the deal

Fees, float windows and merchant agreements are set by the MFS providers and their aggregators and move over time — we deliberately quote no numbers here, because a blog post is not a rate card. What your development partner must get right is the engineering contract above: verification, idempotency, a ledger you own, refund states and a daily difference check. Ask any studio to show those five before they show you a checkout screen.

The same principle runs through everything we build, from courier cash to salon deposits: money is a state, the ledger is the product, and the end of the day should be boring.