We are integrating our online payment system with the paypal IPN transaction notification backend and we got stucked with a problem while testing it with the sandbox:
When using the listener script URL with HTTP it works flawlessly, but when specifying a secure URL it stops working. On the IPN history page (https://www.sandbox.paypal.com/us/cgi-bin/webscr?cmd=_display-ipns-history) all calls made using the secure listener show no HTTP response from our server(!). Direct access to both URL work from a browser.
Our guess is that either IPN calls don't work against secure listeners (we couldn't find a word about this in the documentation) or paypal sandbox IPN servers don't like our IPN listener certificate (which is a free startssl but valid certificate).
Did anyone find something similar or Could provide some advise?
