AES_KEY is not working

Hello. I try to encrypt String.

This is my code.

FString teestclass::EncryptFString(FString OriginalFString)
{
	FString EncryptedFString;
	FString Key = "f";

	if (OriginalFString.IsEmpty())
	{
		UDCLibrary::PrintErrorMessage(this, " : First Empty.");
		return OriginalFString;
	}
	
	int32 Size = OriginalFString.Len();

	TCHAR *String = OriginalFString.GetCharArray().GetData();
	TCHAR *KeyString = Key.GetCharArray().GetData();
	uint8* BytesString = (uint8*)TCHAR_TO_UTF8(String);
	FAES::EncryptData(BytesString, Size);
	TArray<uint8> EncryptedByteArray;
	EncryptedByteArray.Append(BytesString, Size);

	return FBase64::Encode(EncryptedByteArray);
}

[Projectname.target.cs]

public override void SetupGlobalEnvironment(
        TargetInfo Target,
        ref LinkEnvironmentConfiguration OutLinkEnvironmentConfiguration,
        ref CPPEnvironmentConfiguration OutCPPEnvironmentConfiguration
        )
    {
        OutCPPEnvironmentConfiguration.Definitions.Add("AES_KEY=f");
    }

try1.
I used define key on target.cs. and full rebuild.
FAES::EncryptData(BytesString, Size);
This is result after debug my project.

Debug tool always indicate last line.
I think target.cs of AES_KEY is not working.

tyr2.
I used define key on code.
FAES::EncryptData(BytesString, Size, TCHAR_TO_ANSI(KeyString));
This is result after debug my project.

Debug tool always indicate last line.
why ifdef AES_KEY is here??.. .

I want to put AES_KEY in my project.
How Can I put this AES_KEY?..
Thank you for reading.

put this in file Core.Build.cs

Definitions.Add(“AES_KEY="the key"”);