Where can I find the Sheet ID of Google Spreadsheet file

Sheet ID is an identifier of a Sheet in a Google Spreadsheet file.

To obtain it, open the file for the desired Sheet, and locate it at the end of the URL after ‘gid=’ :
https://docs.google.com/spreadsheets/d/1EwXZweUNKKGSC6k6_6IkukyRFeNzi7qEIIjOAC9_vGA/edit#gid=ThisIsSheetID .

Google Sheets API Sheet ID