It comes & goes....you can usually list something then go back & revise later and it will be there?? I have found that it disappears more often according to the category....some categories 'glitch' all the time.
Try another category and see if it's there

If you have sold more than 100 items AND made $12,000 in the last 12 months then you won't see them until you drop under the $12,000. If that doesn't apply to you, as mentioned, go back and revise later. I usually make a note under the ones where the box didn't appear and go back the next day and revise.

 

If I still can't get it to work after a few days, I revise on my phone using the app. It nearly always shows up there. If there's not a promotion running, which often sees it disappear for a few days, I find it can disappear if I list quite a few new items.