[Vuejs]-Firebase Auth rule read if exists in subcollection not working

The way your embedding {clanName} in the get() call is incorrect. Variables are all in $(variablename) format, similar to how you already have $(database) and $(request.auth.uid).

So something like:

if exists(/databases/$(database)/documents/clans/$(clanName)/members/$(request.auth.uid))

Also see:

• The Firebase documentation on accessing other documents in security rules.