If you are seeing blank data (0 cells) coming from your Firebase RTDB job, you likely entered the wrong data path in your Authorize Firebase step.
To test that your data path is correct, try entering this into your browser in Incognito/Private mode (outside Flatly):
https://{yourfirebasedomain}.firebaseio.com/{parentdirectory}/{nodename}.json?&auth={your_database_secret}
If you see data presented in your browser, your data path is correct.
If you do not see any data, something is wrong with the data path you entered into the Authorize Firebase step inside Flatly. Ask your Firebase manager for help.