Tutorial error?

I have followed the tutorial at https://docs.monogame.net/articles/getting_started/4_adding_content.html , but running it gives the error ‘Microsoft.Xna.Framework.Content.ContentLoadException: ‘The content file was not found.’’. Code for Game1.cs below:

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

namespace MonoGame_Test
    public class Game1 : Game
        private GraphicsDeviceManager _graphics;
        private SpriteBatch _spriteBatch;

        Texture2D ballTexture;

        public Game1()
            _graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";
            IsMouseVisible = true;

        protected override void Initialize()
            // TODO: Add your initialization logic here


        protected override void LoadContent()
            _spriteBatch = new SpriteBatch(GraphicsDevice);

            // TODO: use this.Content to load your game content here
            ballTexture = Content.Load<Texture2D>("ball");

        protected override void Update(GameTime gameTime)
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed || Keyboard.GetState().IsKeyDown(Keys.Escape))

            // TODO: Add your update logic here


        protected override void Draw(GameTime gameTime)

            // TODO: Add your drawing code here

            _spriteBatch.Draw(ballTexture, new Vector2(0, 0), Color.White);


The content.mgcb contains the correct file: https://i.gyazo.com/687ee6466ffd12e3aad527d46dfe4936.png
What am I missing here?

Edit1: Solved: Needed to rebuild project solution first.