In order for TSO to find that CLIST, it must be present in the standard CLIST search chain, which is normally set in the TSO LOGON procedure (ddname SYSPROC) or dynamically altered via TSO ALTLIB command when needed.
The sample Endevor CLISTs contain the following statement to set up the search chain before starting the Endevor dialog:
ALTLIB ACTIVATE APPLICATION(CLIST) -
and the following to deactivate the change after having called the dialog:
ALTLIB DEACTIVATE APPLICATION(CLIST)
If you are running Endevor from a CLIST, you need to add something similar.
If you are using no CLIST to enter Endevor, you may want to add CSIQCLS0 to your SYSPROC DD in the TSO LOGON procedure.