Cypress cannot access Angular server, even though it is started on localhost

I have an Angular application, that I start locally via ng serve --proxy-config proxy.config.json and a Cypress set-up that has a baseUrl of http://localhost:4200. After starting the server I can access it via localhost:4200, but not 127.0.0.1:42000 or 0.0.0.0:4200.

The problem is that when I try to start an e2e test in Cypress (no matter which browser selected) I get a CypressError:

`cy.visit()` failed trying to load:

http://localhost:4200/

We attempted to make an http request to this URL but the request failed without a response.

We received this error at the network level:

> Error: connect ECONNREFUSED 127.0.0.1:4200

Common situations why this would fail:
- you don't have internet access
- you forgot to run / boot your web server
- your web server isn't accessible
- you have weird network configuration settings on your computer


Server is indeed running

Why can Cypress not access the application? What can I do, so it can access it?

(Posted as Q&A)

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