Paypal only allows one IPN so I will need to look at a switching php and there seems to be a good one at github so that should be OK. Before I set that up however I do some testing.
Via the paypal developer site you can test an IPN, so I drop in the IPN for my forums:
If I hit that from a browser I get "Request not validated" which makes sense. If I use the paypal IPN simulator:
"We're sorry, we could not send an IPN."
No hints, help or suggestions, just sorry. I have done quite a bit of google searching and can't seem to find a common issue here.
I am on linux and as I said I have another program using an IPN with no problem. Any ideas on how I could work out what the actual problem is?