Hi, would really appreciate some help with the below issue!

I'm trying to set up a simple checkout donation button on my website, and have it link to a default authorize.net receipt page.

However I also have a shopping cart/ecommerce application (Ecwid) running on the same site using SIM.

The shopping cart requires that I set a specific Default Relay Response URL. However this is causing a conlict with the Simple Checkout, and although I've also set a default receipt URL, as long as the Relay Response URL is also set it generates a Relay Response timeout. 

An error occurred while trying to report this transaction to the merchant. An e-mail has been sent to the merchant informing them of the error. The following is the result of the attempt to charge your credit card. 

      This transaction has been approved.

It is advisable for you to contact the merchant to verify that you will receive the product or service.

Deleting the Relay Response URL for the shopping cart fixes the issue with the Simple Checkout, but this then obviously breaks the shopping cart.

Any help/ideas?