IPNs are annoyingly difficult to use. Some accounts simply will not send them until an IPN URL is set, even for transactions that include the notify_url in the

IPNs are annoyingly difficult to use. Some accounts simply will not send them until an IPN URL is set, even for transactions that include the notify_url in the request. You cannot even see the IPN history until you enter an IPN URL, even if it was used through the notify_url param. IPNs that include UTF8 characters will not validate by default in most PayPal accounts. PayPal defaults to Win1252, translates the UTF8 content to Win1252, tells you it's Win1252 and then seems to validate the IPN against the original UTF8 data. I have never been able to validate a Win1252 IPN that had UTF8 content. I've tried iconv, stripping bits, and plain substitutions (ü -> u). Nothing seems to work. This seems to be getting better though. For about 2 months last year they forgot to include a field that had to be added in order to verify the IPN. And you had to iterate through a few different values to see which one was correct. So we got a rash of support tickets asking why our customers were suddenly getting notifications of issues verifying PayPal purchases and were having to manually approve orders. I submitted a ticket after a day of dealing with the issue and got a response about 2 weeks after they fixed the issue. There was no indication of the problem on their status site. The IPN verification service randomly returns INVALID for valid data or simply doesn't work. Sometimes IPNs are delayed. Dealing with the PayPal APIs are far, far harder than their sales sites would have you believe.