Cancel an open invoice. Only invoices in OPEN status can be canceled.
Returns 409 if the invoice is already paid, expired, or in a non-cancellable state.
Merchant API key (sk_m_*). Used for invoice management, store configuration,
and viewing merchant data.
Authorization: Bearer sk_m_abc123def456...Invoice ID (UUID) UUID v4 identifier
"904e9f44-a5a3-4e07-94c9-9c425d6bbe64"