You can not use SUM function on the module which has Time as a dimension. For those we have MOVINGSUM and TIMESUM.
In your case since you are using Weeks-General option you will have to create a Fake Timescale.
You can have this as a hierarchy setup or you can also map it one time
Once done you can use LOOKUP options to pull the values from the module which is dimensioned by Native Time to a module which is dimensioned by Custom Time. But please keep one thing in mind there is no way you can map Custom Day to Native Time Day because there is no option in time Period formatting. So these all numbers will be aggregated at the week level.