Your documentation: 

https://wpdatatables.com/documentation/connect-wordpress-tables-with-google-sheets-api/?utm_source=lite&utm_medium=plugin&utm_campaign=wpdtlite

Is very aged and horribly out of date.  It is not possible to follow any of the instructions since *all* of the Goolge interfaces have changed from your example.  Do you have a more up to date example of setting this up, because what is there fails.

I was able to get it to work.  It was confusing with the flow and the majority of it is correct, I was just frustrated with the effort to get there.