Adding members to a playbook using the API

I can create a playbook using the API: {your-mattermost-url}/plugins/playbooks/api/v0/playbooks but it appears to ignore the member_ids field and only the default_owner_id is used.

"default_owner_id": self.my_owner_id,
"default_owner_enabled": True,
"member_ids": self.member_ids,
"invited_user_ids": list(set(self.member_ids + [self.my_owner_id, self.customer_user_id])),
"invite_users_enabled": True,

I would be very grateful if anyone could show me how to add new members to a playbook via the API?

Many thanks