Have they paid?
You can either send a cancellation request citing Buyer request to cancel, this will refund them their money, refund your seller fee, and your selelr performance is not affected. Found right of the item sold, frrom More Actions. Sending this for a non payment you have to be assured the buyer accepts the cancellation, if they don't you have to wait 10 full days to close it yourself.
Or, if your buyer has not paid within 4 days, you can now cancel that order stating buyer has not paid, applicable fees will be refunded, the item will be relisted unless you choose it not to relist.
This link will explain the procedure fully.
https://www.ebay.co.uk/help/selling/getting-paid/resolving-unpaid-items-buyers?id=4137&st=3&pos=1&qu...
Might be preferable to use a desktop browser, not a mobile browser or app to manage all of the above, too.
