Flutter: error when trying to run app with new firebase dependencies - firebase

Question

I created a simple app with flutter, and I'm now trying to connect it to an online database, namely googles Firebase. I have added the essentials to my build.gradle files:
dependencies {
classpath 'com.android.tools.build:gradle:3.4.2'
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
classpath 'com.google.gms:google-services:4.3.3'
}
and
apply plugin: 'com.google.gms.google-services'
I've also added the google-services.json file to the android/app path, but only after I've added one of their packages to my pubspec.yaml file, namely cloud_firestore: tabbed under dependencies: I got this error when I tried to run the app (when I ran it without only that package it worked):
'''
Note: /Users/pepijnvanderklei/Developer/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.13.5/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
D8: Cannot fit requested classes in a single dex file (# methods: 75778 > 65536)
FAILURE: Build failed with an exception.
What went wrong:
Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives:
The number of method references in a .dex file cannot exceed 64K.
Learn how to resolve this issue at https://developer.android.com/tools/building/multidex.html
Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
Get more help at https://help.gradle.org
BUILD FAILED in 1m 50s
Running Gradle task 'assembleDebug'...
Running Gradle task 'assembleDebug'... Done 111,8s
Exception: Gradle task assembleDebug failed with exit code 1
'''
Does anyone know what going wrong?

Answer 1

When using firebase, you need to update the minSdkVersion inside android/app/build.gradle to version 21:
minSdkVersion 21
By default, Flutter supports Android SDK v16 (Jelly Bean, released 2012), but multidex doesn't really work with Jelly Bean (though, it's possible). Configuring Jelly Bean to work is beyond the scope of this codelab, so we'll change the minimum target SDK version from v16 to v21 (Lollipop, released 2014).
https://codelabs.developers.google.com/codelabs/flutter-firebase/#3