Troubleshooting 2Checkout Invoice ID Not Found Errors
After applying the 7.6 update, and activating the new Inline Checkout feature, 2Checkout recurring payments created in earlier versions of WHMCS are not recorded.
Payments are received into the 2Checkout account, but the transactions are not recorded in WHMCS.
Reviewing the Billing > Gateway Log shows entries with the Result Invoice ID Not Found
Additional logic is required in the 2Checkout module to handle legacy recurring payments after switching to the new mode.
A hotfix has been created which will resolve this error by including additional logic to handle this scenario. It can be downloaded from:
Once the hotfix is applied subsequent 2Checkout recurring payment installments will be recorded in WHMCS successfully with Inline Checkout mode enabled.
Recurring payment installments made after applying the 7.6 update and before applying the hotfix should be recorded manually in WHMCS: https://docs.whmcs.com/Transactions#Applying_Payment_to_an_Invoice