The listing says "Recommended Mattress Thickness: 10''" -- so that's what I bought.

The Q&A says "The recommended box spring height is the standard height which is about 9 inches tall."Samantha from Wayfair on Jul 07, 2021 -- so that's what I bought.

The actual distance from the slats to the bottom of the headboard is 16 inches. Now my mattress doesn't fit on top of the box spring, and juts out several inches past the foot of the bed. I have to buy another box spring so the mattress actually fits on top of the box spring.

It's quite apparent that Wayfair did not check with the producer of this bed before posting the answer to that question, and instead just guessed that a standard box spring will work, because sure, why not?

Beyond Wayfair's error, the headboard is not sturdy, and the pieces were spilled all over the box.