If you are trading goods between Northern Ireland and the EU, you’ll have to select the VAT Treatment as EU - VAT Registered [NI Protocol]. Once you select the VAT Treatment as EU - VAT Registered [NI Protocol] in a transaction, Zoho Books will automatically replace the GB in your VAT Registration Number with XI. So, you don’t have to manually update the VAT registration number.
If you don’t find this VAT treatment listed, you may have to enable NI protocol in your VAT Settings.
and GST filing.