Trying To Use Vba Code To Evaluate Each Row In A Highlighted Selection

I have a worksheet (with if statements) that I throw numbers from a report into and it uses those if statements to calculate the number of items and money earned. The problem is that sometimes employees use different key words for their items so the formulas dont pick them up and this skews their results for the month. Also it's hard to see where someone messed so I'm trying to write a code that reads each row for a given selection and calculates the sum and if that sum is 0 then we can look for where the employee made an error. This is what I have:

Dim RngToSum As Range
Set RngToSum = Selection.Rows
For Each Row In RngToSum
If Application.WorksheetFunction.Sum(RngToSum) = "0" Then
MsgBox "Lets play find the error"
Selection.Rows.Interior.ColorIndex = 3 'red
Else Application.WorksheetFunction.Sum(RngToSum) 0 Then
MsgBox "Congrats there's no errors"
End If
End Sub

The problem with the code is that I want it to read every line and if there's no errors then have it say "congrats no errors" after ALL rows have been checked because right now it pulls a msgbox per row and I don't want to go through hundreds of no error msgboxes. However, if even just one line has an error then have a msgbox come up.

Also there's something weird where this code wont pick up an error for a row if i highlight two rows (one row without an error and one with) but if i highlight just rows of zeros then it'll pick it up.