Payment Processing Issues
Contents
Merchant Gateway Declining or Failing
Take a look in Billing > Gateway Log to see exactly what response your payment gateway is returning and that should indicate what the problem is for you. It would then be necessary to look up the error codes in your payment gateway's documentation or contact their support team for an explanation.
The explanation of common errors are located in the Troubleshooting sections of each payment gateway's dedicated page of the documentation.
Blank Payment Gateway Page
This is usually caused by a double copy of a gateway file in the modules/gateway directory or .htaccess/php.ini or other file not provided with WHMCS in the directory that needs to be removed.
Gateway Module Error: Configuration Function (_config) not found
Starting with WHMCS 7.8, the Setup > Payments > Payment Gateways page will perform a check to ensure that all present gateways in the /modules/gateways folder contain the required *_config function (without it, a payment gateway cannot be used with WHMCS). If any gateways are found to be missing this function, an informational message will display at the top of the page with a list of the applicable gateway files. You can then audit each of them and remove or correct to resolve this. Correcting will involve adding the _config function to the mentioned file and using it to handle the payment gateway settings as per our documentation at https://developers.whmcs.com/payment-gateways/configuration/ . If you are using a gateway provided by a third party developer, it may be necessary to contact them to update the gateway module to fix this.
This can also be caused by unexpected non-gateway files in the /modules/gateways folder, so auditing and removing these may be needed under some circumstances.
User Redirected to Wrong Page on Checkout
If you have customised your WHMCS header template and added or removed a form, you will need to update the forwardpage.tpl template file which by default will submit form 0 or 1 on the page - if you add a form to your header need to add 1 to the forms[x] setting in that file, if you remove one, you need to subtract 1
Invalid Access Attempt
To avoid this error, please ensure you are logging into your admin area using the exact URL defined in Setup > General Settings.
If for example your WHMCS System URL is set to http://www.example.com/whmcs/, you would need to login to your admin area at http://www.example.com/whmcs/admin. If you login at http://example.com/whmcs/admin this can cause the Invalid Access Attempt message (note the www. was omitted).