You must have made an error installing it. You do not even provide details such as Operating System and Manager version.
In any case see https://www.manager.io/server-edition and note:
Can you help installing server edition?
We do not provide installation service. Server edition works as a custom web-server. If you do not have an experience with web-servers, please seek local IT specialist or sign up for cloud edition. Cloud edition is identical to the server edition in terms of features and functionality. The key difference is that the cloud edition is professionally hosted by us, offering a seamless experience without the need for self-hosting.
and;
How do I install server edition?
To install the server edition, download the archive for your operating system and processor architecture. Extract the contents of the archive into your desired folder. On Windows, launch
ManagerServer.exe, and on Linux or macOS, open a terminal, navigate to the folder, and run./ManagerServer. This will launch HTTP server on port 8080 which you can access from your web-browser.
Once you get it to work and put into production, also note that:
How long can I evaluate free trial version?
Free trial on server edition has no time limit. You will see notice at the top informing you of running free trial. When you are satisfied with the software, please purchase product key to register the copy and remove the notice.
Only the Desktop version is free when used in production (i.e. for real). Notice that Server License cost is the same as Cloud Server and that yearly renewal for updates is 50% of that. We use Server Edition ourselves but I would recommend Cloud if only having basic Server Management and Security knowledge.