I am developing Add-in for Excel 2013 and I have created a function in Excel Add-In as below

```
  public string ExcelReturnString()
    {
        return "This is the string: hi";
    }

```

I have used below code to call the function, but it throws an error.

```
Application.Run(ExcelReturnString)

```

How can I call the Add-in function in macro?