Setup a Google Developers Account

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Use or Create an API Key For Sheets at Developer Console

For Your Google Sheet (If not OAuth, You Need to Make it Visible via URL)

Or you will face PERMISSION_DENIED

Enable Google Sheets API

https://console.developers.google.com/apis/api/sheets.googleapis.com/overview?project=YOURPROJECTID

View Metrics

https://console.developers.google.com/apis/api/sheets.googleapis.com/overview?project=YOURPROJECTISCOOL

Access The Data Via NIFI

https://sheets.googleapis.com/v4/spreadsheets/YOURGOOGLESHEET?includeGridData=true&key=YOURKEY

References:

https://community.cloudera.com/t5/Community-Articles/Streaming-Ingest-of-Google-Sheets-with-HDF-2-0/ta-p/247764