If the bullet is coming straight from your camera perspective, the entire trail will be foreshortened by your viewpoint and you’ll see nothing.
That said, you can easily test any trail renderer by putting it in the scene, pressing play, then dragging the object around in the editor, and you will see the trail. Get that working first.
Also, if you post a code snippet, ALWAYS USE CODE TAGS:
How to use code tags: Using code tags properly