Restaurants/stores will only appear on the Deliveroo if they are within the delivery radius of the post / area code the customer has entered on Deliveroo.
Sometimes the delivery radius of a restaurant/store will be reduced when there is a shorter supply of riders, to make sure that your food/product arrives on time and in good condition.
If your restaurant/store is closed it may not appear on Deliveroo. Make sure your opening hours are up-to-date and that you are set to 'Open for orders' on your tablet or in 'Live Orders' on Partner Hub.