I recently ran into some issues with a "Donate" button, when someone completed their transaction and clicked return to site (a thank you page which I created), error 405 appeared.
SERVER ERROR- 405 - HTTP verb used to access this page is not allowed.
It is to my understanding that this is a fairly common error with the Donate button, thankfully the fix is deceptivly simple.
Most likely your thank you page is an html, however I have gotten this to work for cfm as well. All you have to do is make your page a PHP and have paypal redirect the "customer" to the PHP.
For example, if you were using:
http://www.mysite.com/thanks.html
as your redirect destination after the transaction, change the thanks.html into thanks.php and upload it to your domain. Apply the suffix change on your button settings so now they will be directed to:
http://www.mysite.com/thanks.php
Thats it. It's annoyingly simple and I had to figure this out by constantly donating a penny until I found a solution which worked. I hope this helps!
Good luck!
*Note: If they cancel the purchase a .html file extension shsould be fine, a .php extension is only necessary for the completed purchase redirect destination to prevent the 405.
