Records a company expense against a category (and optionally a vendor). Set is_paid: true to also capture a payment for the full amount in the same call — payment.payment_type (or top-level payment_type) is then required and must be a configured payment-method key (e.g. cash, card, cheque, bank-transfer). A method configured with refRequired also needs a reference, and a bank-transfer method with transferReceiptRequired a receipt file; a paid expense missing either is rejected with 422 (payment_reference / receipt_file_id).

Optional purchase tax: send tax_id (and optionally tax_inclusive / tax_amount). amount stays the total payable with the tax included — e.g. {"amount": 530, "tax_id": 1} with a 6% GST returns tax_amount: 30, net_amount: 500, tax_rate: 0.06, outstanding_amount: 530.