MFPLI00138W "entry-name" is a function that has been called by a CALL statement.

Entries declared with the RETURNS attribute must be invoked by a function reference either used in an expression or as the source of an assignment.
Resolution:
Invoke the function "entry-name" by assigning the reference to a variable that can hold the returned value.
Module:
INTRP2.PL1, PRCSCALL.PL1