What's wrong with this Server expression, it gives error "Invalid Expression". Just want to check sy

Server Expression:

SUM( CASE WHEN branch_data.sales_date >= get_max_date()  THEN NULL ELSE  ( CASE WHEN(  (1-(CASE WHEN BRANCH_DATA.SALESPLUS= 0 or BRANCH_DATA.SALESPLUS = NULL  or BRANCH_DATA.utc_final_fc_lag1 = 0 THEN 1 ELSE ABS(BRANCH_DATA.utc_final_fc_lag1 - BRANCH_DATA.SALESPLUS)/BRANCH_DATA.SALESPLUS ) END)<0 THEN 0

ELSE

(1-(CASE WHEN BRANCH_DATA.SALESPLUS= 0 or BRANCH_DATA.SALESPLUS = NULL  or BRANCH_DATA.utc_final_fc_lag1 = 0 THEN 1 ELSE ABS(BRANCH_DATA.utc_final_fc_lag1 - BRANCH_DATA.SALESPLUS)/BRANCH_DATA.SALESPLUS )END)) ) END )

NOTE:

BRANCH_DATA.SALESPLUS   refers to Adjusted History Series

BRANCH_DATA.utc_final_fc_lag1 refers to final forecast lag 1