Hi guys, as Michael wrote.
Just, be sure you have logged in to the Locus Map 4 app under the same account, you used when purchasing Silver. It does not matter which account you used in Google Play, the only important is the account directly in the Locus Map app.
If still no success, contact our team over
https://help.locusmap.app web and share in a ticket your email address so we may check it, thanks.