Charcter Class C++ -> Apply Downward Motion

Hello, I desperately want to apply gravity to my Character C++ Class. I’ve tried everything and got to the point where I use the player’s input function to apply downward movement. Here’s the code:

void AFPSCharacter::MoveX (float axisValue) {

	FVector direction = FRotationMatrix(Controller->GetControlRotation()).GetScaledAxis(EAxis::X);
	AddMovementInput(FVector (0.0 ,0.0, -1.0f), axisValue);
}

The function (obviously) normally moves the character forward/backward but I want to always move the character down, which for some reason doesn’t appear to be happening (FVector (0.0, 0.0 ,-1.0f) ). So, does anyone have any knowledge of why this might be happening (I have obviously compiled and built the project before trying this).