What does this mean for you?
The windsor framework for you as a business will mean that any B2B goods that you ship from Great Britain to Northern Ireland will be subject to restrictions similar to sending from the Great Britain to the EU, where we require specific international data. The requirements which you will be subject too become stricter if you do not have a UKIMS number. I'd recommend reading the official UK Government windsor framework article to fully familiarize yourself.
What is a UKIMS number?
UKIMS stands for UK Internal Market Scheme and you'll be required to have a UKIMS number if you plan on sending B2B shipments to Northern Ireland using the Green Lane. If you do not have one, your shipments will be treated as Red Lane, where your shipments will have harsher restrictions placed on your shipments into Northern Ireland.
Where can I get one?
On this article from the UK government, you will need to read through a number of pre-requisites before you apply for one. Once you have a UKIMS number, you'll want to ensure it's entered in your companies Tax Numbers page along with your EORI number, if it isn't already.
Below I will list the are the shipping restrictions you will face when shipping with Royal Mail. If you have come across this guide but do not ship with Royal Mail, I'd recommend talking to our support team to get a better understanding of what you will need for your respective courier.
You have a UKIMS Number (Green Lane Shipments)
Your shipments will be subject to the normal EU shipping requirements. You are also specifically required to provide a country of manufacture, failure to provide one will result in an error.
You do not have a UKIMS number (Red Lane Shipments)
Your B2B shipments will be subjected to tighter restrictions alongside the normal EU shipping requirements, such as:
- Product commodity codes must be set
- Product country of manufacture must be set
- Shipments are restricted to a value of 135
- A Senders EORI is required
- The recipient address must contain a company name & address line 1
If your shipment fails to pass any of these restrictions your shipment will fail.
Note: B2C shipments will not have this restriction, so it is important when configurating your Royal Mail settings that you appropriately set whether your shipments are bound for residential (B2C) or non-residential (B2B) addresses.
Regardless of whether your shipments are green lane or red lane, it's always the best idea to ensure you have all the data you need setup in Shiptheory when shipping internationally. Within Shiptheory we have a page you can visit to check how much information you already have in Shiptheory and will give you a good idea of what you need to do next. 
From here you can see what your missing, from product level information to tax numbers. This will give you an idea of what you're currently lacking and should you be missing any data that we recommend, there will be some suggestions at the bottom of the page as to how you can tackle this.
After you've made sure your international data is up to spec, navigate to your Royal Mail settings in Shiptheory and enable the Shipping to Northern Ireland setting. You should then configure any of the below settings that you would like to change, do so.
If you have any other questions about this, or need a hand sorting out the international data you can get in touch with our support team!