We are have been made aware of an issue at PayPal processing IPNs, which will impact WHMCS users. PayPal have opened the following event to track the issue:

https://www.paypal-status.com/history/eventdetails/13006

Payments made via PayPal during the impacted period may not be recorded by WHMCS.

• Payments will be received into your PayPal account, but transactions will not be recorded and invoices marked paid.

• The Billing > Gateway Log may not contain any reference to the payment

OR

• The Billing > Gateway Log may show an IPN Handshake Error Result.

The debug data may contain a 500 Internal Service Error towards the end.

1. Transactions can be recorded manually in WHMCS: https://docs.whmcs.com/Transactions#Applying_Payment_to_an_Invoice

2. Once the incident is resolved you may be able to request the failed IPNs are re-sent: https://developer.paypal.com/docs/ipn/integration-guide/IPNOperations/#resend-ipn-messages

When manually entering transactions it is important the PayPal transaction IDs are entered correctly so as to avoid duplication when re-sending IPNs at a later date.