Hi,
I’m not able to transfer ownership of a Sheet. I get this error returned. I am able to allow access to a user.
I also tested in the Live Demo version, and I receive the same error.
Thanks,
Steve
Hi @steve.r.ervin, thanks for reporting this issue.
I’ve passed it to the developer team for research. Once any result will become available, I will let you know asap.
Thank you for understanding.
Regards,
Thanks Serg. Any update on this?
Hi @steve.r.ervin, thanks for checking on this.
The developer team is working on the task. I will let you know asap once as anything will become available.
Regards,
Hi @steve.r.ervin, thanks for your patience 
The developer team checked what could be done in this regard. Regretfully, Google supporting documentation states that Currently Drive does not support changing the ownership for items which are owned by gmail.com accounts; it’s supported for Workspace accounts.
Thus, the developer team renamed the call and the result of the call to: send rights to another user to see the document.
To check changes, please update your plugin to version 1.16.0 - Changed API Call “Transfer Ownership” to “Send Writer rights”.
Please let me know if there is anything else that I can help with about our plugin.
Regards,