Create or retrieve the vendor record with GET /v3/vendors or POST /v3/vendors
Create the AP bill with POST /v3/bills, including invoiceNumber, dueDate, vendorId, and lineItems with GL account mappings
Retrieve available vendor credits with GET /v3/vendor-credits (endpoint added April 2025) and apply them against the bill before payment
Schedule the payment with POST /v3/payments, referencing the bill ID and specifying the payment method and process date
Subscribe to the bill.updated and payment.updated webhook events to track status transitions from open to scheduled to paid
Known gotchas
Vendor credit endpoints are v3-only (released April 2025); they do not exist in the v2 LTS API
Bills submitted via the API bypass BILL's UI-based approval workflow by default unless your BILL account has API approval rules configured — verify your account's approval settings
BILL's production and staging environments use distinct base URLs and credentials; test against staging (gateway.stage.bill.com) before pointing to production
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp