I have also this problem in UE4.26
In version 4.24 I had no problem with this
java.lang.NullPointerException:
at com.epicgames.ue4.GooglePlayStoreHelper$d.a (GooglePlayStoreHelper.java:3)
at com.android.billingclient.api.c.f
at com.epicgames.ue4.GooglePlayStoreHelper.c (GooglePlayStoreHelper.java:10)
at com.epicgames.ue4.GameActivity$z.run (GameActivity.java:1)
at android.os.Handler.handleCallback (Handler.java:883)
at android.os.Handler.dispatchMessage (Handler.java:100)
at android.os.Looper.loop (Looper.java:237)
at android.app.ActivityThread.main (ActivityThread.java:7948)
at java.lang.reflect.Method.invoke (Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1075)