Configure BILL v3 AP vendor payment with ACH and verify NACHA payroll descriptor

Steps

1. List available payment methods for a vendor with GET /v3/payments/options?vendorId={id}&amount={amount}
2. Create an ACH payment with POST /v3/payments, specifying processDate as the next US business day if submitting after 10 AM PT
3. For 1099 contractor compensation payments, include a standardized PAYROLL description in the payment per NACHA rules effective March 20, 2026
4. Monitor payment status by listening to the payment.updated webhook event or polling GET /v3/payments/{id}
5. Handle failed ACH returns by checking the return reason code in the webhook payload and initiating a corrected payment or contacting the vendor