Partial payments without the spreadsheet

In Malawi it is normal for a customer to pay an invoice in two or three parts - some by Airtel Money, some by bank transfer. Tracked in a spreadsheet, the balance drifts: a payment entered twice, a reversal forgotten, a rounding difference that nobody can explain.

Record each payment against the invoice it settles, with its method and reference. The invoice balance should be computed by the system from those payments, never typed in by hand.

Protect against double entry. When a payment is submitted twice - a double click, a retry on a slow connection - the second submission must be recognised as the same payment. InfiCRM does this with an idempotency key on every payment.

Refuse overpayments and keep reversals visible. A bounced transfer should be reversed with a reason, restoring the balance, not deleted.

Do the arithmetic in whole tambala, never with decimals that a computer cannot represent exactly. That is how a 16.5% VAT line and a 5% discount always add up to the same total on the quotation, the invoice and the receipt.