It’s essential that you add a cover photo.

If your website has an identifying image, such as a banner, use that. Otherwise, use an image that readily identifies, or at least is associated with your website.

Hint 1:
Unlike just about every other app that uses images, FB won’t resize your image to fit. FB would like your image to be 828 px by 315 px. Get it as close to that as you can.

Hint 2:
FB will allow you to move your image around within its 828 x 315 frame, so you can get it looking at its best.