Problem with dispatching

I'm returning an item but when I try to mark as dispatched eBay won't accept the tracking number/information leaving me unable to mark the item as dispatched. I've messaged the seller but want to make it official as well.
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If you did not use the eBay label [I'm not sure why you would not] then did you actually open a "return case" in the resolution centre?

 

If you did then there should be a place to enter the tracking. If not then as far as I know there is no way to do so.

 

All returns must go through resolution. Do-it-yourself does not work and - were the seller to refund - he would [stupid though it may sound] be given a defect

 

@abbyhardman