Error: “unexpected token: {” error.

This error can happen if you have an extra {  bracket in one of your merge fields on templates. To resolve, check all fields to remove this extra character. It can also happen if there is some hidden formatting in your template. Try creating a new google doc (do not copy it) and see if document will generate with no issue. If the error is resolved with new template ID, then copy section by section of old template to the new one and there should be no more hidden formatting.