ERROR: 10501 Invalid Configuration This transaction cannot be processed due to an invalid merchant configuration.

Make sure that you have accepted the "PayPal Payments Pro" agreement in your PayPal account after you have been approved by PayPal for PayPal Payments Pro. If you have accepted their agreement but are still getting this error, PayPal also occasionally acknowledges the agreement and activates Virtual Terminal but somehow misses activating PayPal Payments Pro itself; if your PayPal "Get Started" summary screen only shows Virtual Terminal and nothing about PayPal Payments Pro, please contact PayPal support to get your PayPal Payments Pro service activated.

If you are only using PayPal Payments Standard with a regular PayPal personal, Business or Premier account (i.e., if you have not upgraded to PayPal Payments Pro), please go to Seller Admin > Edit Profile where under the Accept Credit Cards section you should select I will accept Credit Cards via PayPal Standard, then click Submit to apply changes.