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A problem occurred evaluating root project 'firebase_auth'. > Could not find the firebase_core FlutterFire plugin

Everything was working smoothly. I tried to add google_mobile_ads package to pubspec.yaml, after adding this package, whenever I run the app it said minSdk version should not be less than 19.
What went wrong:
Execution failed for task ':app:processDebugManifest'.
Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 19 declared in library [:google_mobile_ads] D:\Academic\My Work\Software Projects\My Mates\my_mates\build\google_mobile_ads\intermediates\library_manifest\debug\AndroidManifest.xml as the library might be using APIs not available in 16
Suggestion: use a compatible library with a minSdk of at most 16,
or increase this project's minSdk version to at least 19,
or use tools:overrideLibrary="io.flutter.plugins.googlemobileads" to force usage (may lead to runtime failures)
So I updated the minSdkVersion in android/app/build.gradle from 16 to 19. Now whenever I run the code it says
A problem occurred evaluating root project 'firebase_auth'.
Could not find the firebase_core FlutterFire plugin, have you added it as a dependency in your pubspec?
Though I've updated firebase_auth(^3.0.1) & firebase_core(^1.4.0) to the latest version but nothing worked.
Its weird to see many related questions but without solution. Anyone who encountered the same problem please share how to overcome it and rebuild the app successfully.

Run flutter clean in your terminal.
After that, run flutter packages get again to download the latest packages in your application.

Does using `tools:overrideLibrary` have any benifits over `minSdkVersion`?

I'm going to use a library in my project and it shows error:
Error:Execution failed for task ':app:processDebugManifest'.
Manifest merger failed : uses-sdk:minSdkVersion 14 cannot be smaller than version 15 declared in library [:library:] ... Suggestion: use
tools:overrideLibrary="test.com.library" to force usage
This prompt lets me know that imported liobrary using higher version (15) than my application min sdk version which is 14.
I want to know if I
I want to know if I use tools:overrideLibrary does it let my application to keep its min SDK version and be installed on phones with API14 or it is not the case? Beside I want to know what is the benefit for using tools:overrideLibrary over `minSdkVersion'?

Manifest merger failed while adding FirebaseUI library

My app is targeting sdk 25, with minSdk 14, compiledSdk 25and buildToolsVersion 25.0.0
When I try to add following dependency,
compile 'com.firebaseui:firebase-ui-auth:2.3.0'
It gives: following error
Error:Execution failed for task ':app:processGoogleDebugManifest'.
Manifest merger failed with multiple errors, see logs
when I checked logs of AndroidManifest error:
It shows: uses-sdk:minSdkVersion 14 cannot be smaller than version 15 declared in library
and suggest me to add Suggestion: use tools:overrideLibrary="android.support.customtabs" to force usage.
when I am adding this, it gives various manifest merger errors.
And while finding the solution, someone suggested to chage sdk version to 26, but it also give various error.
I'm just beginner in this, so please help me out.

The error message you posted says it all:
uses-sdk:minSdkVersion 14 cannot be smaller than version 15
Change your minSdkVersion to 15 in order to use firebase-ui libraries.

As you can check here the Firebase UI-AUTH has a dependency with:
compile "com.android.support:customtabs:26.0.1"
Here you can find the official doc and you can check the same in the Manifest inside the library:
This package requires API level 15 or higher.
You can't change the minSdk required for a library and you can't have a minSdk = 14 if you use this library.
I read that it is not a option for you, but currently the minSdk=15 covers over the 99% of the distribution.
Here the updated distribution:
https://developer.android.com/about/dashboards/index.html

Android Studio / Eclipse import error

I am here with a simple problem. I have created a game project in one of the game builders (BuildBox) and now, when I try to import and convert it into an .apk, I get this error:
Error:Execution failed for task ':app:processDebugManifest'.
Manifest merger failed : uses-sdk:minSdkVersion 11 cannot be smaller than version 14 declared in library [com.google.android.gms:play-services:10.2.1] C:\Users\Rob.android\build-cache\8f9b56554d0082e5d885287503f760ae18c8f99a\output\AndroidManifest.xml
Suggestion: use tools:overrideLibrary="com.google.android.gms.play_services" to force usage
The problem is that I am an absolute newbie with Android Studio and I have no idea how could I update the "minSdkVersion" from 11 to 14.
I will appreciate any help!
Thanks a lot!

Edit your build.gradle file of app module in your application, and look for "minSdkVersion" parameter in defaultConfig block.
Just change it to your suitable version.

Manifest merger failed : uses-sdk:minSdkVersion 11

I really don't know what's the problem, I always get this error when I try to build my project
Error:Execution failed for task ':app:processReleaseManifest'.
Manifest merger failed : uses-sdk:minSdkVersion 11 cannot be smaller than version 14 declared in library [com.google.android.gms:play-services:10.2.0] C:\Users\AYOUB\Desktop\Boiling ball studio\app\build\intermediates\exploded-aar\com.google.android.gms\play-services\10.2.0\AndroidManifest.xml
Suggestion: use tools:overrideLibrary="com.google.android.gms.play_services" to force usage

As stated in the error; you should update your minimum version from 11 to 14.
Google Play services need at least Android version 14 (4.0) to work.
Check this link from Google

Manifest Merger occurs when there is a mismatch in a version of your dependencies. So be careful to mention the version of your dependencies to be same.
And also make sure that the version is same in all the external libraries or a module, you are using.