I noticed that you have opened a Support ticket on the same topic. I have answered your questions there. I will summarize my response also in this thread for the benefit of our community.
The detail section of any data item is rendered as many times as the number of records you have in the corresponding data source. The data scope in the detail section is the current data record, i.e. a single row of data. Therefore, the Sum
function will aggregate over this single value and will return the value itself.
What you need to do is to add a Static group to the data item. The scope of the static group contains all the data in the data item (its parent). The group header and footer sections are rendered only once. Hence, you may place the aggregate function in the group footer to display the total once for the entire Table/List.
The attached report demonstrates the approach.
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