PWX supports OCCURS DEPENDING ON n
PWX supports OCCURS n TIMES
PWX does not support other forms of OCCURS.
I would recommend raising a support ticket to get help with this.
Also, please note that in mainframe-speak, a file is either FIXED or VARIABLE. There is no FIXED VARIABLE.
I would recommend getting that clarified before opening a support ticket.
Given that an OCCURS is involved: OCCURS n TIMES may be FIXED or VARIABLE, depending on what else is in the copybook, while an OCCURS DEPENDING ON is always VARIABLE.
If you are dealing with one of the 80s era base+displacement type files (Fidelity and EDS were common users of this practice, but not the only ones), then it is almost certainly VARIABLE, and probably not usable with PWX without involving consultants.