code: func (b *Bot) Accept(query *PreCheckoutQuery, errorMessage ...string) error {
  	params := map[string]string{
  		"pre_checkout_query_id": query.ID,
  	}
  
  	if len(errorMessage) == 0 {
  		params["ok"] = "True"
  	} else {
  		params["ok"] = "False"
  		params["error_message"] = errorMessage[0]
  	}
  
  	respJSON, err := b.Raw("answerPreCheckoutQuery", params)
  	if err != nil {
  		return err
  	}
  
  	return extractOkResponse(respJSON)
  }
docs: // Accept finalizes the deal.