To start a TSO/E address space for the BCM Web API server from z/OSMF, the CEA (common event adapter) must be running in full function mode. Use the console to run the F CEA,D command, and then make sure that STATUS is ACTIVE-FULL in the output CEA004I message.
If STATUS is not ACTIVE-FULL, run the F CEA,MODE=FULL command to change to full function mode.
In addition, do not set 0 for the MAXSESSIONS parameter (the maximum number of TSO/E address spaces that can be started via z/OSMF) of the CEA startup parameter CEAPRMxx parmlib. You can check the current value of the MAXSESSIONS parameter by checking the ALLOWED value in the CEA004I message that is output by running the F CEA,D command.