Project failing to build

Hello,
First many thanks for this excellent tutorial.

I have forked this project, created the required Google Service to support it, using the package name com.musevisions.multipleCountersFlutter. However, when I try to run the app I see the following errors:

java.lang.IllegalStateException: Dex archives: setting .DEX extension only for .CLASS files
at com.google.common.base.Preconditions.checkState(Preconditions.java:456)
at com.android.builder.dexing.ClassFileEntry.withDexExtension(ClassFileEntry.java:64)
at com.android.build.gradle.internal.transforms.DexArchiveBuilderTransform.removeDeletedEntries(DexArchiveBuilderTransform.java:274)

I am attempting to build using VSCode.

Plus many more of a similar nature.

Can you help to resolve this?
Sid