Vat "Code: Paid" - Where Does This Go On Packages?

I have added this CODE PAID line with the reference number on several things headed off to Australia and the ebay shipping address seemed to be straight forward but for the life of me I can't recall where this line went (and can't find an old invoice). Today, I have to send something off to the UK and have a similar line to now add but ebay's shipping address is a wee bit confusing. I have always actually struggled a bit with figuring out how to write UK addresses and this just added to my head scratching. Here is an example, with identifiers changed to something random:

Jimithy Beam
Flat 221, Sesame Street,
Barrington Crescent GB 999 9999 99 Code:Paid
Barkham
Berkshire
SP3 5TM
United Kingdom


Any advice on exactly how to write this on a package properly? Do I do it exactly as shown with the VAT code basically on the same line as the address? Also, do you tend to combine the village and county or write on separate lines as ebay has it? And final question, do I need to include an invoice or packing slip on the outside of the package or can I still just keep those inside?

Sorry for the rather newbie questions but I tried Google first and could not find much conclusive or that I could comprehend lol, particularly the VAT code line piece.

Thank you in advance!!

I have always combined the town & county on a single line, similar to how you'd do it for US/Canada. They've always arrived. No idea on the other questions, sorry.

Your address lay-out is correct, although Flat 221 and Sesame Street should be on separate lines. That code bang in the middle of the address looks likely to confuse the post office. I'd have it entirely separate from the address.

Maybe invoice inside, customs declaration outside?

I've always gone to ebay's order page and clicked on 'purchase shipping label' and used the format that they show. Without purchasing the label. So far they all seem to have made it.