The following value expression for placeholder works in html type input in the table header
= Sum(CDec(Fields!TotalDueAmount.Value))
But when I change it to concatenate a string it doesn't work. I tried below both of them shows #Error
= "Total: " + Sum(CDec(Fields!TotalDueAmount.Value))
= "<b>" + First(Fields!TotalLabel.Value, "ModelData") + ": " + "</b>" + Sum(Fields!TotalDueAmount.Value, "ModelData")
You need to convert the sum back to a string to concatenate it with other strings:
= "Total: " + CStr(Sum(CDec(Fields!TotalDueAmount.Value)))
An even better option is to use a placeholder. Type "Total: " in the textbox and then right-click in the textbox after it. Select the option to create a placeholder. Set the Value to Sum(CDec(Fields!TotalDueAmount.Value))
. Now you can adjust the number formatting on the placeholder independently.