From eBay:

"Click & Collect orders

When a buyer chooses Click & Collect, we’ll automatically update the address to show their selected ParcelPoint or Hubbed store address. We’ll also add a unique 8-digit eCP code.

All you need to do is pack and send as usual — making sure you clearly display the eCP code on the parcel so it can be easily processed at the Click & Collect location. 

We’ve got you covered

As long as you post your item in your stated handling time, send it to the address with the unique eCP code, and upload tracking details (or the item arrives to the collection point), we’ll protect you from any issues like negative or neutral feedback, or defects. 

If a buyer doesn’t collect their item within 7 days from when we’ve let them know it’s ready, they can’t claim their item wasn’t received. We have a team focused solely on supporting our Click & Collect service, so please get in touch if you need a hand."

I suggest you check the label and make sure the identifier is clear.

Contact eBay and let them know the parcelpoint address was marked as incorrect/ undeliverable.

Refund- less postage if you can and suggest to buyer they can rebuy with a different address or take it up with eBay .