Declare goods that you're moving to or from Northern Ireland using the Trader Support Service (TSS).
The Trader Support Service has been updated to help businesses manage customs and safety declarations for goods moving between Great Britain and Northern Ireland. This free service is available to businesses, hauliers, and individuals responsible for making these declarations. If your business is already registered, existing users must invite any additional staff members to join the account. New users must register through the service portal to begin submitting declarations and managing duty payments.
Source: https://www.gov.uk/guidance/declare-goods-that-youre-moving-to-or-from-northern-ireland-using-the-trader-support-service-tss. Summarised automatically from the official source — general information, not advice.