You completed the authentication process and Google sheet integration process, but still, your contact form entry not showing in selected Google sheet?
Don’t worry, go to the integration tab, there you can see, Debug Log option, under this option you can see View and Clear option. Click on View option to see, why GSheet Connector adds-on not working in your site.
If Debug Log is empty, but GSheet Connector Addon not working.
Process 1) Then you have to enable debug as true in wp-config.php file
define( 'WP_DEBUG', true );
Process 2) Enable all Debug True
Note: If you enable all Debug Log true, then you will able to see all the errors of your site. Make sure you will disable all Debug Log after GSheet Connector add-on issue will be solved.