You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: create_activity_id.go
    path of file: ./repos/weapp/updatablemessage
    
    the code of the file until where you have to start completion: package updatablemessage

import "github.com/medivhzhan/weapp/v3/request"

const apiCreateActivityId = "/cgi-bin/message/wxopen/activityid/create"

type CreateActivityIdRequest struct {
	// 非必填	为私密消息创建activity_id时，指定分享者为unionid用户。其余用户不能用此activity_id分享
    
func (cli *UpdatableMessage) CreateActivityId(req *CreateActivityIdRequest) (*CreateActivityIDResponse, error) {

	api, err := cli.combineURI(apiCreateActivityId, req, true)
	if err != nil {
		return nil, err
	}

	res := new(CreateActivityIDResponse)
	err = cli.request.Get(api, req)
	if err != nil {
		return nil, err
	}

	return res, nil
}