Installing Control-M/Enterprise Manager or Control-M/Server with an Oracle 19c database fails with the false message:  The host has refused your TCP/IP connection.

Full error message seen both on screen and in the installation logs:
The host has refused your TCP/IP connection. Verify that the connection properties are correct, and that the connection is not being blocked by a firewall.

Communication to the Oracle listener is working properly from the Control-M host.
For example on Linux the following command works properly and shows communication or firewall is not the issue.

nc -zv oracle_listener_hostname 1521

Control-M is using an older version of the OJDBC client that the Oracle server is rejecting.

Alternate Solution:
Newer versions of Oracle require a newer version of the Oracle JDBC client.
Control-M by default is using the ojdbc6.jar file which is being refused by Oracle 19c
1) Download from Oracle the version ojdbc8.jar for your specific OS
2) Place the ojdbc8.jar file in the installer directory structure within Setup_Files\lib
3) In the Setup_files\lib directory, backup the current ojdbc6.jar file
4) Rename the ojdbc8.jar file placed into Setup_Files\lib in step 2, to ojdbc6.jar
This step is to replace the current provided ojdbc6.jar file with the newly downloaded ojdbc8.jar file, but it is necessary to rename it to ojdbc6.jar so the Control-M installer recognizes it.

5) Run the installer again


Tracking Information:
CTM-9426 has been created for this issue and will be implemented in a future release