Android Question Uncaught translation error: already added: Lcom/google/android/gms/common/util/VisibleForTesting

Hi,

I'm trying to update my project to use Firebase Messaging. I'm using B4A 9.00 and Firebase Notifications 1.21, and targeting API 28. I've managed to overcome a 'no virtual method subscribetotopic' issue, and I'm now targeting API 28 not 27 after getting 'ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:fontVariationSettings' error on compile. I'm now getting this error now that I'm targeting API 28.

B4A Version: 9.00
Parsing code. (0.03s)
Building folders structure. (0.76s)
Compiling code. (1.94s)
Compiling layouts code. (0.72s)
Organizing libraries. (0.00s)
Generating R file. (0.37s)
Compiling debugger engine code. (3.53s)
Compiling generated Java code. (14.54s)
Convert byte code - optimized dex. Error
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/common/util/VisibleForTesting;
1 error; aborting

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Can anybody advise on what I'm doing wrong? I've looked for duplicate jars but cannot find any although that apparently is the cause. Some pointers would be really helpful.

Thanks all,

Richard