Well it certainly helps to place a working example next to your own code in error. I spotted a slight problem.
"EXCIO * DISKR IN_FILE (FINIS STEM stemvar." Mine
"EXECIO 3 DISKR MYFILE (FINIS" CorrectStarring me in the face the whole time. Spelled it correct in the title…before I wrote this!
However it still complains about the FINIS.
Also I learned I could do…HELP EXECIO
Ready; T=0.02/0.03 19:53:37
q cmslevel
VM/370 CMS Community Edition Version 1 Release 1.2
Ready; T=0.01/0.01 19:53:42
q cplevel
SYSTEM 4381-A
VM/370 Community Edition Version 1 Release 1.2 07/19/22 13:20:46
IPL at 19:22:34 GMT MONDAY 08/21/23
PEAK LOAD= 005 USERS
Ready; T=0.01/0.01 19:53:59