It is a bit confusing on the GAS UI that it has a copy button for the ID on App Script > Project Settings page, however, it doesnt let me save until I found out the real ID.

As shown below, to get your ID (at least my case), after deployment or manage deployment, you can get the version number and the ID, here is the tricky part that the ID you get here on the URL is different with the one from the copy button.