Sorry to hear you’re having trouble ordering, that won’t do.
Make sure the place you’re trying to order from is open. If it is, double-check that you entered any personal and payment details correctly. Another thing to look at is the restaurant’s or store's minimum order value. Some places won’t allow you to order unless you spend a minimum amount.
If none of the above does the trick, you can always try using a different web browser or the Just Eat app on your smartphone.