When you enter a address/country in the address section within the customer information the country will then appear on the invoice. The country code will also then populate on the VAT 101 report.
See attached as to how it shows up in the Invoice to section.
According to HMRC VAT rules:
5.2 Invoices to other EU member states
If you send an invoice to a person in another EU member state you must also show:
1. the letters ‘GB’ in front of your registration number for cross border supplies
2. the registration number of the recipient of the supply preceded by the alphabetical code of the relevant EU member state
When in Sage the same invoice would show the Tax Registration as BE[removed] but in Quickbooks it doesnt add the BE (although this DOES show up when I run the VAT 101 report)