I (THE NEWBIE) would like to know, how to use the in TT Europe offer to upgrade to TT Go Mobile, more or less "free"? - if possible!

My TT Europe is a "Creative/for-test-purpose-only" version, installed from a Apk!

When I launch TT Europe I get "the offer" to upgrade to TT Go for a pair of Cents -- BUT when I click on the "Get offer", Iím meet with a dialogue box stating something like
"This version of the application is not configured to be invoiced via Google Play" (Very bad translation to English!)

Is there a way, any help will be appreciated??

Cheers - and thanks in advance - (and, apologies for my bad English, I do hope this makes sense :-))