Can’t connect to a Prefect Server from other machine despite port 4200 being open

First, check that the API is working on the Server deployment by going to the Interactive API and testing that the API is healthy. The hello endpoint can be used as follows:

query {
  hello
}

If it is working, it means that you need to start the Server with the --expose flag as follows:

prefect server start --expose

This will allow outside connections. You can find more information in this Github issue and this documentation page.