10501 accepted account admin agreement approved cart configuration credit default due error help installed invalid merchant paypal paypal-pro preferences pro process processed sale setting standard switch transaction

After I installed your cart I got only one sale so I tried a test today. When to process with Credit card I got this:" 10501 Invalid Configuration This transaction cannot be processed due to an invalid merchant configuration.
Error"
What invalid configuration I did? Can you help me?

If you are using PayPal Pro, please make sure you have accepted the merchant agreement in your PayPal account after your Pro account has been approved.

If you are not using PayPal pro, please switch to PayPal standard in Admin > Cart Preferences (that is the default setting).