How to get the preview_image_url for all streaming interactive avatars

https://docs.heygen.com/reference/streaming-avatar-list allows us to retrieve a list of the currently available streaming avatars. However, it only provides a small number of data points for each avatar.

We then have https://docs.heygen.com/reference/retrieve-avatar-details that allows us to retrieve further details for each avatar, which includes the preview image.

However, a lot of the avatars that are in the streaming avatar list, return 404 for the retrieve-avatar-details endpoint.

Am I missing something?