Hierarchy Summary

Anplanners, 

I have a Module (XYZ) Dimensioned by GL (Row Headers), Cost Centers L3 as selectors and few Line items to determine the total amount. Aim is to get input at GL level for each Cost Center.  

I have a summary module (ABC) which is NOT dimensioned by any LISTS and simply has to take the high level total of the above module. 

However when I link the line item from ABC Module (SUMMARY MODULE/DIMENSION LESS MOUDLE) to that of XYZ (INPUT MODULE/DIMENSIONED BY COST CENTER L3 and GL), its throwing an error which says Cost Center L3 does not have a "built in top level" 

How do i come around this issue ? I thought Cost Center L2, Cost Center L1, would automatically summarize Cost Center L3, however that does not seem to be the case.

How do I get the total value to Module ABC ?
Thanks