HUB, RestAPI, add existing user to group Follow

Hi all.

Can't add user to group in hub. I know Group ID, User login and User ID.

https://www.jetbrains.com/help/hub/HUB-REST-API_User-Groups_Users-of-User-Group_Add-User-to-Users-of-a-User-Group.html

I trying to:

curl -X POST https://hub.XXXXXXXX.ru/hub/api/rest/usergroups/56d36ddd-332c-3935-8182-d7f9e1e87782/users\?fields\=login -H "Authorization: Bearer perm:Xxxxxxxxxx=.yyyyyyyy==.VasdjuiuIUHuidhfguihi" -H "Content-Type: application/json" --data '{"login":"hubUserLogin"}'

but I got the error:

{"error":"Internal Server Error","error_code":500,"error_description":"child.id must not be null","error_developer_message":"child.id must not be null","error_uri":"https://www.jetbrains.com/help/hub/2018.2/HUB-REST-API.html"}

I must sent as a body the ALL users object?!

Thanks.