When performing an action which involves invoices or transactions (such as placing an order, viewing an invoice, or viewing invoice and transaction lists in the Admin Area) the following Oops! error displays:

Error: Module Not Found

Going to Configuration > System Settings > Payment Gateways will also display an error:

The Payment Solution module could not be loaded, most likely because it has been removed. You should deactivate it now.

You have activated and configured the payment gateway, but the corresponding file is missing from the /modules/gateways/ directory.

There are two possible solutions:

1. Restore the missing module file to the /modules/gateways/ directory. You may need to upload the file to your server via SFTP or restore from a backup.

2. Deactivate the missing module and switch customers to a different payment gateway module. For more information, see Deactivating Payment Gateway Modules.