The Sheet should be public and Anyone with link can view. Example:

https://docs.google.com/spreadsheets/d/{spreadsheetId}/edit?usp=sharing

If you dont want to create a key you can use this URL format (which downloads a json.txt file of the format):

• https://docs.google.com/spreadsheets/d/{spreadsheetId}/gviz/tq
• https://docs.google.com/spreadsheets/d/{spreadsheetId}/gviz/tq?sheet={sheetName}&tq=select+*+Where+A=27938

Or configure a key as per the Official docs.

1. Go to Google Console and create a project (or use an existing one)
2. Goto Credenetials page and create a API Key
3. Include Sheets API from library

You can now get json using URL Format:

With the V4 pattern, the spreadsheet needs to be shared as File > Share > Share with others > anyone with the link can view.

https://sheets.googleapis.com/v4/spreadsheets/{spreadsheetId}/values/{sheetName}?alt=json&key={theKey}