Automated Invoice-to-Payment-Voucher System

The problem

Finance teams processing supplier invoices were doing it the traditional way: opening each invoice, manually reading the payee details and line items, working out VAT and withholding tax by hand, and typing the results into a payment voucher template. For a country like Tanzania, where VAT and WHT rates depend on whether a supplier is VAT-registered, what kind of service was provided, and whether the supplier is local or foreign, this is easy to get wrong: and every mistake means a wrongly calculated payment or a compliance risk with the Tanzania Revenue Authority (TRA).

What we built

A Django-based system where staff upload an invoice (single or in bulk), and the rest of the process runs automatically:

• AI extraction: a vision-capable AI model reads the invoice image and pulls out the payee, line items, amounts, and supplier residency signals (address, currency, bank details).
• Tax engine: applies Tanzania's tax rules based on what was extracted: 18% VAT for registered resident suppliers, and withholding tax at 2–15% depending on whether the supply is goods, general services, rent, or professional/consultancy fees; with separate rules for foreign suppliers.
• Voucher generation: calculates subtotal, VAT, WHT, and net payable, writes the amount out in words, and generates a payment voucher document per client, using each client's own template and branding.
• Approval workflow: vouchers start as drafts and move to approved; once approved, they're locked from edits or deletion, so there's always a clean audit trail.
• Background processing: invoices are queued and processed automatically, with failure tracking and retry counts so nothing silently falls through the cracks.
• Multi-client access control: each client's invoices and vouchers are only visible to the staff assigned to that client.

Results

The manual, error-prone parts of the workflow i.e. reading invoices, calculating tax by hand, retyping data into a voucher, are now automatic. Staff review and approve rather than compute from scratch, and every approved voucher is protected from later edits, giving the finance team a reliable audit trail they didn't have before.