Hello,
All users were informed with an app message, you probably missed it somehow, but don't worry you can still migrate your accounts.
Please read this article:
https://aquamail.freshdesk.com/a/solutions/articles/77000550192The Pro Unlocker is obsolete and must be deleted from your device.
To migrate look for this icon in the "Inbox" folder.
Make sure you are logged into Google Play with the account that you originally purchased Aqua Mail with (remove other accounts from the Google Play store, make sure you only have 1 account logged in).
The migration license is tied to your account. Make sure you are using it in Google Play and install Aqua Mail with it. Add the account to Aqua Mail and the app will switch to a Pro version.
Let me know how it goes.