The problem with the 500 error is that it is a general error, "something" is wrong but its not clear what. I had the same error when people wanted to pay with paypal, for me the solution was to change the permission codes in my files map (back office from your web hosting).
Go to your file manager (in your web hosting account) and go to the map domain, public_htm file and check what permission code they are set. For me it worked when putting the map paypal to 755 or 777. im not sure if its safe but for me it works. in the map "modules" is one also called "bankwire" that is the one you need to check.