Http request with custom port

Hello everyone,

i am trying to set up a logic flow to send the submitted form data to my api webservice.
However, this webservice has an endpoint listening on a custom port (not port 80 or 443), but some random number like 16456.

When I run the test to complete the http request block setup the response is always code 400 - connect ETIMEDOUT.

using Postman I am able to connect to the api webservice using the custom port.
When I change the port of the endpoint to the default port 443, webflow is able to connect to the endpoint.

Is there any limitation in WebFlow regarding the port numbers of the webservice port numbers that can be used?

Kind regards