error CS0117: 'Marshal' does not contain a definition for 'SecureStringToGlobalAllocUnicode'

Hello,

Just want to check if Marshal.SecureStringToGlobalAllocUnicode(SecureString); is supported in .NET 4.5 . I keep getting the above error that Marshall doesnt contain a definition for SecureStringToGlobalAllocUnicode .

https://video2.skills-academy.com/en-us/dotnet/api/system.runtime.interopservices.marshal.securestringtoglobalallocunicode?view=netframework-4.5#System_Runtime_InteropServices_Marshal_SecureStringToGlobalAllocUnicode_System_Security_SecureString_
This is the code that I was using, which is giving the error.

using System.Security;
using System.Runtime.InteropServices;

            IntPtr valuePtr = IntPtr.Zero;  
            try  
            {  
                valuePtr = System.Runtime.InteropServices.Marshal.SecureStringToGlobalAllocUnicode(SecureString);  
                exportedString = System.Runtime.InteropServices.Marshal.PtrToStringUni(valuePtr);  
            }  
            finally  
            {  
                Marshal.ZeroFreeGlobalAllocUnicode(valuePtr);  
            }