ERR_PAYMENT_PENDING on Xero: Payment pending. Root cause: Payment still being processed by payment gateway or bank and not yet confirmed as settled. Systems requiring confirmed payment block further processing until status changes from pending to cleared. Step 1: Check payment status in accounting system. Go to Invoices > Payments or Transactions > Payment History. Search by invoice, customer, or date. Click payment record and check Status field. Should show "Pending", "Processing", "Cleared", or "Failed". If "Pending" or "Processing", not confirmed by bank yet. Step 2: Check payment gateway or bank portal. Log in to payment processor (Stripe, PayPal, Square, etc.) or bank portal. Search using payment reference or amount. Check transaction status — should show "Completed", "Settled", "Pending", or "Failed". Note timestamp and messages. If completed in gateway but pending in accounting, sync delay may exist. Step 3: Wait for standard settlement period. Most processors take 1-3 business days to settle. Credit cards typically 2-3 days. ACH transfers typically 1-2 days. Check processor documentation for expected time. If within normal window, wait. Do not reprocess or contact support yet. Step 4: Verify payment amount and invoice match. Compare payment received to invoice due. Check for discrepancies (e.g., paid $95 but invoice $100). If amounts do not match, payment held as "pending" until confirm partial payment or request remaining balance. If match, proceed to next step. Step 5: Contact payment processor if stuck. If pending more than 3 business days, contact processor support. Provide transaction ID, amount, date, customer details. Ask to check status and manually settle if possible. They may investigate if payment failed due to fraud checks or holds. Step 6: Manually mark payment as cleared if necessary. If processor confirms settled but system shows pending, manually update status. Go to payment record and click "Mark as Cleared" or "Confirm Payment". This updates invoice to "Paid" and allows further processing. Document reason for manual update in notes.