If you're using SQL Server 2019 GM Build, please upgrade your SQL server to build CU4 or above version as there is a known issue with SQL server 2019 GM which affects the communication with Apex Central.
Access the Apex Central and do the following:

1. Reduce the client TCP/IP socket connection timeout value from the default value of 240 seconds:
   1. Start Registry Editor.
       

      Always back up the whole registry before making any modifications. Incorrect changes to the registry can cause serious system problems.

       
   2. Browse to this registry hive: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters.
   3. Create a new REG_DWORD value named "TcpTimedWaitDelay".
   4. Set the value to "30".
2. Extend the Socket Port number by opening Command Prompt with admin privileges and launching the following command:

   netsh int ipv4 set dynamic tcp start=25000 num=30000

3. Reboot the machine.
4. Try to register the Apex One server to the Apex Central server again.