PayPal gateway has rejected request. This transaction cannot be processed due to an invalid merchant configuration (#10501: Invalid Configuration).

If you’re seeing this error message on PayPal with magento, the chances are that you haven’t got the right type of PayPal account.

You will need website payments pro which in the UK attracts a £20 per month user subscription fee.

To resolve the error log in to PayPal and go to the following page

https://www.paypal.com/uk/webapps/mpp/business-setup-standard

Look towards the bottom of the page to apply for the right type of account.