Android flutter project's Firebase notifications working in "test on device" mode but not in production

Question

I'm pretty new to mobile development and took over a project based on flutter 5 months ago. I fixed couple of bugs of the application and published it on markets afterwards.

For a good period of time, I was able to send notifications for both iOS and Android versions of our app before updating flutter and firebase libraries. After updating the libraries, I pushed the new version only for Android and notifications stopped. I'm able to send "test on device" notifications to my device but no luck with the actual campaigns. Also after I updated the libraries, I needed to update the signing for the app.

Here are the things I tried:

1. As I changed the app signing, I got the new App signing key certificate fingerprint (SHA 1) from Google play console and inserted it in firebase. But I didn't remove the old one as I am not sure how to proceed. You can see it here

2. I updated Firebase SDK in any case. As shown in Firebase instructions And put the new google-services.json to app folder here. After I did this, instructions told me to sync the gradle. I couldn't find this button on Android Studio (Android Studio Bumblebee | 2021.1.1 Patch 2) so I tried couple of different approaches I found here to sync gradle. I got "Task wrapper not found in project :app" and as a solution

   task wrapper(type: Wrapper){ gradleVersion = '7.1' }

With this I synced the gradle and created a new apk to test on my device, but again it didn't work.

I hope I've given enough info about the issue. I may be missing crucial details so if you can lead me I'll be glad to share more.