API cannot locate avatar/template

HeyGen API cannot locate my private avatars or private templates. I am receiving the following output error in my n8n workflow "The resource you are requesting could not be found. Avatar ("avatar_id") not found or no longer available."

I have sent a request to the List Avatars API endpoint and received a valid response - the template is there. But once I send the request to the generate video endpoint, i get the error.

I have confirmed I am using the same API token for all requests and that the avatar exists under my single HeyGen account.

Can I please get some clarification as to why this isn't working?

Thanks.