Ultimately it depends on how the DMZ is setup, and on the firewall rules. I would assume that if a default deny policy is in place you wont be able to just spin up a tcp server on the DMZ and be able to connect to it from the outside or the inside.

You would likely be able to access the server from other servers on the DMZ and certainly locally, so it is easy to test if it's a codding problem or network problem.

If it's a network problem, you will need help from the network administrator.

Tiago