Jetztzahlen — Invoice activation — Invoices can be activated or deactivated via PUT/PATCH /rest/invoices/:invoice_number using the active flag. Deactivating an invoice stops its payment link and blocks further e-mails. amount and active can only be changed while the invoice is pending and has never had a payment plan attached. Creating or importing an invoice with an existing number in the same channel automatically deactivates the previous active invoice. Number-addressed endpoints always resolve to the active invoice (falling back to the most recently created). An invoice with an active payment plan cannot be deleted until the plan is cancelled. See Jetztzahlen, Update Invoice, and Delete Invoice.