Show the business profile used on quotes and invoices (name, currency, tax rate, terms).

Change business details. Only the fields you pass are changed.

Add a new client. Returns the client with its id.

Search clients and see what each has been invoiced, has paid and still owes.

Full details and balances for one client.

Change a client's details. Only the fields you pass are changed.

Create a quote (estimate) for a client. Totals and tax are calculated for you.

Create a draft invoice. Use mark_invoice_sent once it has gone to the client.

Mark a quote as accepted and create the matching invoice (same items and tax).

Record that a quote was sent, accepted or declined.

Record that an invoice was sent to the client (it then counts towards overdue reports).

Cancel an invoice that has no payments. The record is kept with the reason.

Everything about one quote or invoice: items, totals, payments, balance, overdue days.

List invoices, newest first, optionally filtered by status, client or overdue.

List quotes, newest first.

Record money received against an invoice. Overpayments are refused.

Who owes money past the due date, grouped by how late (1-30, 31-60, 61-90, 90+ days).

Invoiced vs collected by month (drafts and voids excluded), money still outstanding, top clients.

Write a payment-reminder email for an unpaid invoice. Draft only: nothing is sent.

Save a quote or invoice as a PDF file and return where it was saved.

The audit log: what changed, and when.