I go into my account settings on the Plex app on my android device, I can see the option to buy the Plex pass but no button to unlock app. Just sign out.
Pretty sure it’s not already unlocked as no purchase in Google showing and okay stops after 1 min.
I was checking the settings\account where the only option was to subscribe to Plex pass or sign out.
I’d missed the activation option when playing music! Duh… All working now.