Get all member in a group of current user login

Dear,

Can you show me how to get a list of all member in a group of current user login.

Frist, I try to create a session (external API) : ../API/system/session/1 to get the user ID

Second, I create a UserGroup (External API) : ../API/identity/membership?p=0&c=10&f=user_id={{session.user_id}} to get the group ID.

and then, from group ID, i can get all member in that group ID by create a Members (External API) : ../API/identity/user?p=0&c=100&f=group_id={{UserGroup.group_id}}

But seem like I do something wrong :( it return nothing.