Postman - Add user to Group

I am having trouble adding users to groups via API in Postman.

I’m successful in using the below request when putting in a static group and username:

/api/v1/groups/${groupId}/users/${userId}

When trying to use postman Runner, I’m having trouble having the service run and reference the CSV file.

Anyone have some pointers?

I am trying to figure out how to add multiple users to groups via Runner CSV as well.