Hey Jason, thanks for reporting.
Indeed it's that the Autotask Runtime doesn't have the newest version of the defender relay client. I've sent a PR to update it so it should be out by the next release (during the week). In the meantime I'd recommend using the Open Source code we have for the client, and calling directly to the API endpoint, since the endpoint is working.
Only do that if it's strictly needed, we'll be releasing soon with the update anyway.