Callable SQL used in Equation

I created a callable SQL however it errors due to missing expression.

Here's what the SQL looks like:

SELECT DL_TOTAL_LOAN_BATCH
FROM (SELECT NVL(SUM( A.OFFER_AMOUNT), 0) DL_TOTAL_LOAN_BATCH
FROM PS_PKG_BATCH_AWD A, PS_ITEM_TYPE_FA C
WHERE A.BATCH_SEQ_NBR = (SELECT MAX( B.BATCH_SEQ_NBR)
FROM PS_PKG_BATCH_AWD B
WHERE B.INSTITUTION = A.INSTITUTION
AND B.AID_YEAR = A.AID_YEAR
AND B.ACAD_CAREER = A.ACAD_CAREER
AND B.EMPLID = A.EMPLID)
AND C.EFFDT =
(SELECT MAX(C_ED.EFFDT) FROM PS_ITEM_TYPE_FA C_ED