Nigel,
See also my reply to your other thread.
You haven't said you have a Bridge fitted, so I'm assuming you are running an original 'home built' as opposed to a PAW 'Classic' - which is the name given to the Kit which was first commercially released in May 2016.
If this is the case, what type of License are you trying to obtain? There is currently no option to renew an expired license as the licenses for pre-registered original home-built PilotAware units were automatically extended to May 2017 when the 'Classic' Kits were first introduced, so no new licences have yet reached their expiry date. Lee can 'extend' or transfer your original license manuallly if there is a valid reason to do so. if this is the case you need to PM him (Admin).
At present, licences are issued with Classic Kits in which case the relevant number is the MAC address of the Raspberry Pi, or on purchase of an RF Bridge, in which case the serial number is supplied with the Bridge.
Regards
Peter