If you have ebay's simple delivery enabled you are supposed to use their postage label. If you've bought your own label you have paid the extra cost yourself.
To get it marked dispatched you need to contact ebay to get the tracking number for the item changed to the one on the postage you bought. You can use callback on here: https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid