code: func (c *Conversation) Next() bool {
  	if c.err != nil {
  		return false
  	}
  	if c.firstRun {
  		c.firstRun = false
  		return true
  	}
  
  	insta := c.inst
  	body, err := insta.sendRequest(
  		&reqOptions{
  			Endpoint: fmt.Sprintf(urlInboxThread, c.ID),
  			Query: map[string]string{
  				"cursor":            c.lastItemID(),
  				"direction":         "older", // go to upper
  				"use_unified_inbox": "true",
  			},
  		},
  	)
  	if err == nil {
  		resp := threadResp{}
  		err = json.Unmarshal(body, &resp)
  		if err == nil {
  			*c = resp.Conversation
  			c.inst = insta
  			if !c.HasOlder {
  				c.err = ErrNoMore
  			}
  			return true
  		}
  	}
  	c.err = err
  	return false
  }
docs: // Next loads next set of private messages.
  //
  // See example: examples/inbox/conversation.go