Upgrade to premium failure

For the second time in a row I am having same problem …the app works for a month or so and then reverts back to the free edition and doesn’t allow me to upgrade to the premium one for which I have a license valid ip to December 2018…I get following message … License not found check Google play primary account… App: Avast mobile antivirus 2018 …

https://forum.avast.com/index.php?board=66.0