Indeed that did work and I'm now capturing a PP express id of some sort and storing it successfully. BUT - (and this should be easy!) i'm getting back a different number than the transaction id that is shown in the paypal email.
It looks like I may be getting 'pnref' rather than 'transactionid'. I'm not sure and it seems a little confusing.
The value I'd like to get is the one that is shown in the pp email and in the pp account that is badged up as 'Unique Transaction ID' and is 17 characters (rather than the 12 character one I'm currently receiving).
Hopefully you'll know what I'm talking about. :)