Symptoms
PREP_PROCESS can´t be used on z/OS to pass command to the operating system.
Resolution
Using a JOBS in z/OS adjusting the command and the library can be used as a workaround.
//*----------------------------------------------
//* CHECK JES SPOOL UTILIZATION
//*----------------------------------------------
//STEP01 EXEC PGM=UCCONCMD,
// PARM='"$D SPOOL"'
//STEPLIB DD DISP=SHR,DSN=UC4SCJ.UC4900A.UCXJM25.LOAD
//SYSPRINT DD SYSOUT=*