Generally the way I do this kinds of things is create manual running totals. Running totals as created in the Designer do not work with Formula Fields.
I would create formula hdrAmounts and place it in the page header or group header as may be appropriate. I am not sure it you are trying to total one or two amounts but I would declare a shared variable for each one. In this example x and y.
It would look something like this:
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WhilePrintingRecords;
shared currencyvar x := 0;
shared currencyvar y :=0;
---------------------------------
Above I set each value at 0 so it resets to restart with each run of the page. You suppress this formula.
In the detail section I create a formula called dtlAmount. In it your will need to create the logic for the variables.
It might look something like this:
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WhilePrintingRecords;
shared currencyvar x;
shared currencyvar y;
If paidAmt <> 0 then x:= x + {paidamount_field}
else y:= y + (rateAmount_field};
y;
----------------------
You can suppress this formula unless you need it to show.
In the group footer create a third and final formula ftrAmount that simply returns the variable or the sum of the two variables if needed.
It might look something like this:
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WhilePrintingRecords;
shared currencyvar x ;
shared currencyvar y;
x := x+y;
x;
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You need to clean up the logic on this but hopefully you will have enough information to get started.
You will find additional information in CR Help go to index look under "Running Totals - using formula section "
Hope this is what you needed and that it helps.
Regards;
John W