I'm working in Paypal sandbox mode with the Membership plugin, and am able to successfully register a person and then make a payment that all seems to work fine. IPN is fine. All seems fine.
The transaction even appears to be completed in the gateway transactions report (http://cl.ly/image/1u0i3x2r001h).
However, the member is NOT being upgraded to premium. They just stay at the basic visitor level that they are defaulted to when they're registering (http://cl.ly/image/1g0d2t0N2C2h).
What's confusing me is that they payment goes through, and the site and Paypal seem to be communicating enough to say the transaction is posted. And I'm even able to refund transactions and the gateway transactions report reflects everything. It all seems fine.
So what are possible reasons that the member is not being made Premium despite all this? I've hunted through the forums and can't find a scenario such as this where everything seems successful otherwise.