Full Error Message: 
“Sorry, the file you have requested does not exist. Make sure that you have the correct URL and the file exists.”

-This error message may happen when trying to “edit template” within document action template builder.

How to Resolve:
-Check your sharing settings in Google Docs template and make sure not set to “private.” See this Google Docs article for more detail on choosing your sharing settings though most popular setting is “anyone with the link” under “Advanced” sharing settings.
-If you are accessing the template from a Google Drive folder (meaning you put Folder ID in document action), you need to make sure the sharing settings are modified on the folder as well. You need to have edit access to the folder in use or be owner of the folder if you would like to generate documents there.
-If you need more information on google drive or doc sharing settings, you can this article.