What does the BillingClient have to do with MobileAds?

Question

This is the second time that my app reports this crash in Firebase:

java.lang.VerifyError: Verifier rejected class z4.m: com.android.billingclient.api.Purchase z4.m.j(java.lang.String, java.util.List) failed to verify: com.android.billingclient.api.Purchase z4.m.j(java.lang.String, java.util.List): [0x52] return-object returns a non-reference type Precise Constant: 1 (declaration of 'z4.m' appears in /data/app/ku.myapp.myapp-os8JbpuKflSLMLcYsXNb5g==/base.apk)
    com.google.android.gms.ads.internal.client.zzej.zzw(zzej.java:6)
    com.google.android.gms.ads.MobileAds.setRequestConfiguration(MobileAds.java:1)
    com.easyapps.cryptnote.application.MyApp.onCreate(MyApp.kt:33)
    android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1162)
    android.app.ActivityThread.handleBindApplication(ActivityThread.java:6717)
    android.app.ActivityThread$H.handleMessage(ActivityThread.java:2020)
    android.os.Handler.dispatchMessage(Handler.java:112)
    android.os.Looper.loop(Looper.java:216)
    android.app.ActivityThread.main(ActivityThread.java:7625)
    java.lang.reflect.Method.invoke(Method.java:0)
    com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
    com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)

In my MyApp.kt I initialize this the MobileAds:

val configuration = RequestConfiguration
            .Builder()
            //.setTestDeviceIds(testDeviceIds)
            .build()
MobileAds.setRequestConfiguration(configuration)

Additionally, I do not know if the app crashes when this issue occurs since I can't reproduce it.

What does the BillingClient have to do with MobileAds?