C# GPUParticles2D type or namespace name could not be found

Hello everyone.
I am very new to Godot, which by the way I am enjoying a lot.
I have encountered an issue I can't figure out how to solve, so any help will be valued.

This C# line throws and error stating "The type or namespace name 'GPUParticles2D' could not be found:
GPUParticles2D particles = GetNode("GPUParticles2D") as GPUParticles2D;

I am using the Godot namespace:
using Godot;
using System;
using System.Collections.Generic;

Edit: I am using Godot Engine v4.1.1.stable.mono.official