Got it sorted, was just some incorrect settings in paypal. Never really used paypal so reading through all their documentation was a bit of a chore but got there in the end.
For the record it was this:-
1. wrong API in epayment_method (still had the sandbox one in there, doh!)
2. wrong IPN address in paypal.
all the a2b settings were correct.
so for anyone else reading this, the following still work (taken from star2billings page)
https://secure.paypal.com/cgi-bin/webscrssl://www.paypal.comThe above was with non ssl (so port 80), i'll test with ssl later as i do have ssl enabled on the site, i just wasn't using it to get paypal working.