User permission in group

Hi
Version my gitlab is 10.6
I would like to ask about user permission in group.
To check it, I am using API_POINT:
/groups/:id/members/:user_id
Sometimes, I receive: { “message”: “404 Not found”}. After checking members this group, I am not a member this group.
My question is: Why I see that group without my user, when I run: /api/v4/groups/ ??

Br,

Hi,
I resolve the issue.
API v3 is receiving group which my user is a member.
BTW, I am curious, why I see a few addional group in v4 API.

Have a nice day.
Br,