During the client creation process and from the Client Settings page, you can select whether a client is VAT registered.
Enabling this feature will mean any invoices that are uploaded to Luca that include VAT, will have the VAT rate and values extracted from them automatically. Custom VAT rates can be used as well as selecting from the standard 5% or 20% rates in our VAT rate drop down on the invoice detail page.
If a client does not have the VAT registration feature enabled, any invoices that are uploaded and include a VAT component will not see this reflected when publishing to Xero or QuickBooks. The invoice totals will still be accurately extracted but the VAT amounts will intentionally be left as 0 and this VAT amount will be allocated equally between the line items.