Sum total of column in rdlc report footer

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C#

RDLC

I have dataset1 contains : ( name - price ) in rdlc report and textbox1 placed in the footer of the report. I tried to sum the total of column (price) but I get error :

> Severity Code Description Project File Line Suppression State
> Error
> The Value expression for the text box ‘Textbox1’ references
> report item 'price' in an aggregate expression with a scope. A scope
> is not allowed on aggregates in the page header or footer which
> reference report items


how to sum the column price and show the result in textbox1 in the footer ?

What I have tried:

here is the expression I used :

=SUM(reportitems!price.Value, "dataset1")