Avatar Default Voice Not Being Used in API Video Agent

Hi HeyGen Team,

I’m currently making an API call where I explicitly specify the avatar ID and instruct the Video Agent to use only the default voice attached to that avatar.

In my prompt, I clearly state:

“Make sure you use the default voice attached to this avatar ID: [avatar_id]. Do not use any other voice.”

However, the generated videos are still using random voice narrators from the HeyGen voice library instead of the avatar’s configured default voice.

Is there a better way to enforce this through prompting?
Or is there a specific API parameter that must be set to ensure the avatar’s default voice is always used?

I’d appreciate any clarification on best practices for locking the default avatar voice when using Video Agent via API.

Thanks in advance