Email notifications are not receiving

I am working with Elastic alerts (with Webhook) and I need to receive an email notification when a new alert is created. Using the fields shown in the following link (Integrations | GitLab), if I mention someone in the description parameter, the issue is created and added in to-do list, but email notification does not arrive.
Creating an issue manually, I can assign someone with: /assign @user. As the link above says, we can also add other parameters. How can I assign an alert to someone with Elastic (Webhook)?