Your CSS looks correct, however you only shared the CSS and not the HTML itself. The most common cause of this CSS not loading your image is empty body element. Body element by default has no height of its own and background image is a CSS property so it would not affect the height of body element on its own. A background image applied on empty body element would not show on the screen. I feel this might be the issue as otherwise there is no issue with your CSS (unless the image does not exist).

If that does not work, please respond with answer to following

Does it work without background-attachment: fixed?

Is the path of image relative to CSS file or HTML file?

Try adding some content to body element or share more info.