Is EXECUTE PROCEDURE legal syntax in Informix-4gl? Typing your code into Genero I get 'The cursor "PROCEDURE" has not been declared in this program'.
For us it would be something like
PREPARE s FROM "execute function motor:p1(?)"
EXECUTE s USING aa
see more at https://4js.com/online_documentation/fjs-fgl-manual-html/#fgl-topics/c_fgl_sql_programming_010.html