Buyer says unable to purchase as I've excluded their area from posting

[992hollywood]

The buyer lives in Guernsey and it's not showing as excluded on my listing as per photo so I don't know how to adjust it so they can purchase

[**peaseblossom**]

It's usually to do with Evri because they charge more for the channel islands, whereas Royal Mail charge the same as UK postage.    You can remove Evri as an option here:
https://www.ebay.co.uk/ship/prf

If you can't revise the listing after that you may have to end it and relist afterwards so the buyer can buy using Royal Mail.