1. Confirm the transaction in the bank or gateway account. Match the amount, currency, customer and invoice reference.
2. Search WHMCS Transactions List for that transaction ID. Check whether it was allocated to another invoice or credited to the account.
3. If a gateway callback failed, repair and reconcile the notification path before entering a duplicate manual receipt.
4. If the payment is genuinely missing from WHMCS, record it through Add Payment or the appropriate transaction workflow.
5. Confirm the resulting balance and any provisioning, renewal or unsuspension action.

Review who performed the action and whether the amount was intentionally waived or settled using account credit. In WHMCS 9.0, marking an invoice paid while a balance remains can create a credit note. The ledger therefore matters when investigating why the displayed amount due reached zero.

Do not delete the adjustment or fabricate a bank transaction to make the record appear paid correctly. Have the billing owner determine whether the intended result is a documented allowance, a correction or a new amount to collect, then use the supported workflow.

Check the provider's final dispute or reversal result and whether WHMCS already processed it. The Reverse Payment workflow can change due dates and service status, while domains and custom items require separate review. A refund, payment reversal and invoice cancellation are different actions.

After correction, compare the client balance, invoice ledger, transaction list and service dates. Add an internal explanation identifying the original error and the verified result. This prevents a later administrator from attempting collection again based on only one screen.

• Record an offline payment against the correct WHMCS invoice
• Correct a WHMCS invoice without losing its audit trail
• Troubleshoot WHMCS payment callbacks and unpaid invoices
• Process and reconcile a WHMCS refund

• WHMCS billing logic
• WHMCS credit and debit notes
• WHMCS payment reversals
• WHMCS transactions