Well the issue is right in here:
“My site received PP emails – Post Payment Verification failed”
All you need to do is check what is failing (this will give you indication as to what you are doing wrong) and fix that. When a post payment verification fails it will also say why it failed in that email… what failed in your case?
Sandbox emails won’t get routed as they are not real emails where emails can go from the outside workd (sandbox puts the receipt emails there as a simulation)