Unable to DELETE in isql using JOIN

Question

I've got a SELECT statement built that properly identifies records I wish to delete. My syinvolv table is a linking table that associates two primary keys (one from nmmain and prmain in my example)

SELECT count(*)
    FROM syinvolv 
    LEFT JOIN prmain ON syinvolv.relrec = prmain."number" 
    LEFT JOIN nmmain ON syinvolv.rec = nmmain."number" 
    WHERE prmain.ownerid != syinvolv.rec AND prmain.ownerid != nmmain.aka;

However, isql appears to be unable to handle the syntax when switching to DELETE

DELETE
    FROM syinvolv 
    LEFT JOIN prmain ON syinvolv.relrec = prmain."number" 
    LEFT JOIN nmmain ON syinvolv.rec = nmmain."number" 
    WHERE prmain.ownerid != syinvolv.rec AND prmain.ownerid != nmmain.aka;

I tried DELETE FROM syinvolv, DELETE syinvolv FROM syinvolv, I finally tried chatGPT assistance which suggested a NOT EXIST statement but that altered my data set so the SELECTED records were incorrect. Any ideas?