Where have I gone wrong on this CN22 declaration and why could it have been refused by customs?

We only expanded our business into e-commerce last summer and into the Autumn selling on eBay and Amazon. I only wanted us to sell in the UK only whilst learning the ropes, but as Amazon launched in Ireland, we had quite a few sales over there.

We were unclear on customs declarations at the beginning and sent our first few parcels without them. We were filling them in on Royal Mail but not attaching them to the parcels. Some arrived to the recipient, others were returned to us.

This parcel above was one of the returned ones. As soon as it arrived back to us, I added the CN22 declaration as shown, re-labelled the parcel and posted it back out.

The recipient messaged me just after Christmas saying he hadn’t received the item. I refunded him and told him if it turns up, please just keep it as an apology for the long delay and our initial mistake.

It’s just arrived back to us this morning and I’m really unsure as to why? Would anybody be able to shed some light?

I’d love to expand into Europe and internationally but not until I’m confident we’re doing everything by the book and understand the processes properly.