I am trying to work with the PayPal IPN simulator to get my development underway.
It's very confusing in the sense that some documentation/form inputs require HTTPS and others don't. It seems the production website will accept HTTP but not the simulator.
So, what exactly are the requirements here?
When I pass either a HTTP or HTTPS url into the simulator I get the following error
IPN was not sent, and the handshake was not verified. Please review your information.
That error makes it sound like some kind of SSL is required. As a side note, the request, doesn't get as far as my API (I can't see anything in the logs).
IPN simulator works with http too. As an alternate, you could try to use your IPN URL in your simple html buy now button code (sandbox) and check if you get the IPN notification(in case if IPN simulator is down)
<input type="hidden" name="notify_url" value="YOUR_IPN_URL">
It might be that your IPN listener file does not accept the GET/POST requests or any HTTP error for that matter can be seen inside your IPN history logs.