Hello could you help me I get this error FirebaseError Previous value was empty
Show the value and the database so we can point at the issue
I’m not sure but will suggest that the issue is because you are trying to append a tag but you don’t have that tag in your database
Maybe as a test try using the “store value” block to make sure you have the database set up correctly
If it is working fine then this should confirm my theory and you should just add the tag into the database before hand of course I’m not sure what your application is or what it does but hopefully this would work
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Thank you very much, that’s why I get the error
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glad I could help 
mark the reply as the solution so people will know the topic got solved 