Update the payment status of an invoice created in the Access Point Provider integration. The
invoice must already be signed.

PARTIAL may be sent repeatedly until the outstanding balance is settled. A PARTIAL payment that
clears the balance settles the invoice, so the invoice is stored and returned as PAID rather than
PARTIAL, is reported to NRS as PAID with no amount, and is queued for fiscalisation. Sending PAID
against an invoice that is already settled is accepted and changes nothing.