So I can call my IPN handling page (an aspx page) happily using Fiddler to POST a fairly accurate version of what the IPN should be sending, and it works fine. However, as soon as I use the IPN test tool or try a 'real' transaction it throws a 405:
2012-01-25 18:46:55 193.128.120.227 POST /paypal_notify.aspx - 80 - 173.0.82.126 - 302 0 0
2012-01-25 18:46:55 193.128.120.227 POST /403_error.htm - 80 - 173.0.82.126 - 405 0 1
I just can't figure it out. Calling an ASP page from IPN works fine but ASPX and ASHX both throw 405s. And yet POSTing to the page myself isn't a problem.
If anyone's got any ideas what might cause this I'd be really grateful!
Well, you first do a redirect to an error page. Paypal tries a POST to /403_error.htm and since that should probably be a GET you get the 405. Something is probably wrong in your paypal_notify.aspx in the first place.
403 means forbidden, so do you have any security scheme that throws the 403?
You might want to post the code you use in paypal_notify.aspx so we can figure out what is causing the 302 to the error page for 403.