Invitation to beta test prerelease of Composer 21

Hello Mark
I don't know whether this the right place to ask,but I have great difficulties ordering and purchasing the upgrade version of Composer for
Notation Musician (2.0.4)that I already own.I tried twice and did receive the order code on my E-mail address,but when returning to the order form, the key turns out to be invalid.So I must have done something wrong again.Could you please show me the right procedure for
the right upgrade ?
Regards
Djim