How to add text to an existing shape(textbox) in C# Excel Interop

I have an excel which contains textboxes/shapes which I am going to fill in with specific data. I used the following code in identifying each shape:

//using Excel = Microsoft.Office.Interop.Excel;

Excel.Worksheet xlWorkSheet
foreach(Excel.Shape shp in xlworksheet.Shapes)
{
    //code to add text to shape goes here....
}

I also tried using:

shp.TextFrame2.TextRange.Characters.Text = "Test";

and

shp.TextFrame.Characters(Type.Missing, Type.Missing).Text = "Test";

but gives an error which states The specified value is out of range and Member not found. (Exception from HRESULT: 0x80020003 (DISP_E_MEMBERNOTFOUND)), respectively.

What should be the correct approach in adding texts to existing textboxes?

You have to check if the type of Shape is msoTextBox before setting text.

Excel.Worksheet xlWorkSheet
foreach (Excel.Shape shp in xlworksheet.Shapes)
{
    if (shp.Type == Microsoft.Office.Core.MsoShapeType.msoTextBox)
    {
        shp.TextFrame.Characters(Type.Missing, Type.Missing).Text = "Test";
    }
}