Sending lead quickemail via API

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Your softwarees
My Mautic version is: 7.2.16
My PHP version is: 7.2.16

Problem
Hi Guys

Our goal is to send transactional Email with custom content (custom subject, custom body) were all URL’s in the body content should be tracked by Mautic.

The UseCase works over the Mautic WebInterface, but I’ve found no way via the API yet.
Directly in the Web Interface Mautic allows to send me single email to a contact. Internal it’s called “lead_quickemail”. How can this behavior be used via the API?

Is there’s always an email template required in the API? As using this endpoint works, but needs an existing email: https://developer.mautic.org/#send-email-to-contact

Thanks for any hint