This issue is resolved and new 12.1 versions is available in play store. Please update the app to resolve the issue.
Google deprecated an api related to ads we were using in our app. Few users using the non-premium version of the app got affected by this. We have uploaded a new version (12.1) to android play store having a fix. Google has a review process before apps can go into production. The time taken for review seems very unpredictable ranging from few hours to days. It seem to be more of days now than hours.
If you are affected by this issue and want an immediate solution, please download and install the apk directly.
The apk can be downloaded from here -
IMPORTANT: DO NOT uninstall the existing app, you will lose your data .. just use below procedure and it will upgrade the existing app.
Android by default prevents installing apps from outside play store so you will need to temporarily give permission. Instructions on doing that here -
Here's our play store status to add some faith :(
Complaints on long review times in play store - https://www.reddit.com/r/androiddev/comments/sb7hxb/long_review_times_for_google_play_review/