[Samba] samba-tool cannot add or remove group members

[Sébastien QUESSON]

samba-tool group addmembers domaingroup 'SAMDOM\user1'
ERROR(exception): Failed to add members "SAMDOM\user1" to group "domaingroup" - Unable to find "SAMDOM\user1". Operation cancelled.

samba-tool group addmembers 'SAMDOM\domaingroup' 'SAMDOM\user1'
ERROR(exception): Failed to add members "SAMDOM\user1" to group "SAMDOM\domaingroup" - Unable to find group "SAMDOM\domaingroup"

samba-tool group addmembers localgroup 'SAMDOM\user1'
ERROR(exception): Failed to add members "SAMDOM\user1" to group "localgroup" - Unable to find group "localgroup"