A buyer cannot cancel an order only request one.
Why does the seller wish to cancel? Are you agreeing to this?
End of the day for whatever reason, you cannot make a seller post out a paid for item, but it seems here the seller wishes for your permission to cancel, as that way they will not receive a damaging defect for not honouring the sale.
Up to you how you wish to proceed, you can accept, or deny the request and state you want your item posted, but then you'd be left with waiting one day after the item's last estimated date for delivery to open a case for item not received, and another 3 full days to escalate the case if necessary for a refund.
As said, what is their excuse for wanting to cancel the order ?
@sam49l-252
