Problem with JavaScript /API-Workflow

Hey, guys.
Here’s my problem. I send mails via an external mailer and send the record for the content of the mail to the mailer via JavaScript.
If the user send the mail via JavaScript everything works as it should. But I also send status mails, which should also be executed via JavaScript. These mails should then be sent via End-Point-API in the menu “API Workflows”. No more mails arrive there. However, the required data record is created. (Workflow seems to work).
Can it be that JavaScript does not work in the API workflows?

Friendly greetings