How to send notification mail to a specific user's email from the server side through the API?

You’d want to use the Create Event call to send a custom event to just one profile (assuming you also have a flow triggered off that event). All of the SDKs support this method. Include in the event properties any custom properties you’d want to include in the flow’s email.

Thank you so much for the answer.

I followed this and was able to send a notification email but I faced two issues.
1. The custom properties I added while creating the event are not reflected in the email or I am not finding a right way to add the properties in email template. 
 

 const createEventInput = {
      data: {
        type: 'event',
        attributes:   {
          // the below properties are not showing up in the email.
          properties: {
            notification_title: 'This is notification title',
            notification_content: 'This is notification content.',
            content: 'hi, this is content'
          },
          metric: {
            data: {
              type: 'metric',
              attributes: {
                name: 'Web notification'
              }
            }
          },
          profile: {
            data: {
              type: 'profile',
              attributes: {
                email: 'sample@example.com'
              }
            }
          }
        }
      }
    }

2. The email is being sent only once per profile, but my use case is to trigger the flow as many times the user triggers the event ! 
    

Please help me with the answers. Thank you.

thanks for the answer. 
When I follow this approach, I am facing two issues: 
1. The flow will be triggered only once for one profile, but I need to send the notification mail each time when I Create Event for a profile. 
2. The custom properties are not showing up in the mail which are set while creating a event.

Thank you so much, yes metric-triggered flows will fire for a profile each time the profile gets that event. The smart sending feature was on because of that while testing for a single profile the email was not being sent multiple times.

also {{ event.property }} syntax worked perfectly.✌🏽🙌