code: func ListContacts(c *messagebird.Client, groupID string, options *ListOptions) (*contact.ContactList, error) {
  	query, err := listQuery(options)
  	if err != nil {
  		return nil, err
  	}
  
  	formattedPath := fmt.Sprintf("%s/%s/%s?%s", path, groupID, contactPath, query)
  
  	contacts := &contact.ContactList{}
  	if err = c.Request(contacts, http.MethodGet, formattedPath, nil); err != nil {
  		return nil, err
  	}
  
  	return contacts, nil
  }
docs: // ListContacts lists the contacts that are a member of a group.