android app crashes after unity screen (maybe because of AdMob?)

Hi everyone,

I'm testing my game on my One Plus 5T, and it crashes after unity splash screen. I tested my game on a Galaxy Note 3, and it crashes the same way. I can't find a working solution.
I have used logcat to spot the problem. Here is what I get:

01-01 22:37:37.419 18053-18072/? I/art: at void com.admob.plugin.AdmobUnityPlugin.() ((null):-1) 01-01 22:37:37.419 18053-18072/? I/art: at com.admob.plugin.AdmobUnityPlugin com.admob.plugin.AdmobUnityPlugin.getInstance() ((null):-1) 01-01 22:37:37.419 18053-18072/? I/art: at boolean com.unity3d.player.UnityPlayer.nativeRender() ((null):-2) 01-01 22:37:37.419 18053-18072/? I/art: at boolean com.unity3d.player.UnityPlayer.c(com.unity3d.player.UnityPlayer) ((null):-1) 01-01 22:37:37.419 18053-18072/? I/art: at boolean com.unity3d.player.UnityPlayer$c$1.handleMessage(android.os.Message) ((null):-1) 01-01 22:37:37.419 18053-18072/? I/art: at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:98) 01-01 22:37:37.419 18053-18072/? I/art: at void android.os.Looper.loop() (Looper.java:154) 01-01 22:37:37.419 18053-18072/? I/art: at void com.unity3d.player.UnityPlayer$c.run() ((null):-1) 01-01 22:37:37.445 18053-18053/? D/AndroidRuntime: Shutting down VM 01-01 22:37:37.446 18053-18053/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.PaulEmileGiacomelli.PortalCube, PID: 18053 java.lang.Error: FATAL EXCEPTION [main] Unity version : 2017.3.0f3 Device model : OnePlus ONEPLUS A5010 Device fingerprint: OnePlus/OnePlus5T/OnePlus5T:7.1.1/NMF26X/11280212:user/release-keys

                                                Caused by: java.lang.NoClassDefFoundError: Failed resolution of: Lcom/google/android/gms/ads/AdSize;
                                                    at com.admob.plugin.n.a(Unknown Source)
                                                    at com.admob.plugin.g.run(Unknown Source)
                                                    at android.os.Handler.handleCallback(Handler.java:751)
                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                    at android.os.Looper.loop(Looper.java:154)
                                                    at android.app.ActivityThread.main(ActivityThread.java:6422)
                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                 Caused by: java.lang.ClassNotFoundException: Didn't find class "com.google.android.gms.ads.AdSize" on path: DexPathList[[zip file "/data/app/com.PaulEmileGiacomelli.PortalCube-1/base.apk"],nativeLibraryDirectories=[/data/app/com.PaulEmileGiacomelli.PortalCube-1/lib/arm, /data/app/com.PaulEmileGiacomelli.PortalCube-1/base.apk!/lib/armeabi-v7a, /system/lib, /vendor/lib]]
                                                    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
                                                    at java.lang.ClassLoader.loadClass(ClassLoader.java:380)
                                                    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
                                                    at com.admob.plugin.n.a(Unknown Source) 
                                                    at com.admob.plugin.g.run(Unknown Source) 
                                                    at android.os.Handler.handleCallback(Handler.java:751) 
                                                    at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                    at android.os.Looper.loop(Looper.java:154) 
                                                    at android.app.ActivityThread.main(ActivityThread.java:6422) 
                                                    at java.lang.reflect.Method.invoke(Native Method) 
                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

01-01 22:37:37.446 18053-18053/? D/AppTracker: App Event: crash 01-01 22:37:37.450 1391-3049/? W/ActivityManager: Force finishing activity com.PaulEmileGiacomelli.PortalCube/com.unity3d.player.UnityPlayerActivity 01-01 22:37:37.454 1391-3049/? D/OemPhoneWindowManager: [isDefaultHome] default home: ActivityInfo{99b5e5f net.oneplus.launcher.Launcher} 01-01 22:37:37.457 18053-18053/? I/Process: Sending signal. PID: 18053 SIG: 9 01-01 22:37:37.457 3075-3373/? D/OPReportService: addMonitorFolder onEvent path=data_app_crash@2018-01-01-22_37_37_456.txt, event:128 01-01 22:37:37.482 1391-2035/? W/InputDispatcher: channel '4d6b14d com.PaulEmileGiacomelli.PortalCube/com.unity3d.player.UnityPlayerActivity (server)' ~ Consumer closed input channel or an error occurred. events=0x9 01-01 22:37:37.482 1391-2035/? E/InputDispatcher: channel '4d6b14d com.PaulEmileGiacomelli.PortalCube/com.unity3d.player.UnityPlayerActivity (server)' ~ Channel is unrecoverably broken and will be disposed!

I guess it has to deal with AdMob, but what is the problem? How can I fix this?

Thank you for your answer.

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