I am not able to assign a group to a node while creating it We are using Drupal 7.39 and Services 7.x-3.12 .

We are also using organic groups 7.x-2.7 and while creating a node of type attendance (which is a group content). We are not able to assign a group to it.

We are passing the following parameters:

{
  "type": "attendance",    
  "title": "Testing Attendance",  
  "field_attendance_status":{  
  "und":{  
    "tid":3  
  }},  
  "og_group_ref":{  
    "target_id":16  
  }  
}
I have tried posting group content but didn't work in all field widgets (select, checkbox or auto complete)

I see there exist an issue with that field og_group_ref take a look at that question have an answer with a patch hope to solve the issue.