No, you do not have to add VAT rate to the invoice yourself.
VAT is calculated by our system automatically based on the customer details and the VAT number that you input. In case you're invoicing a company who has an EU VAT number then the VAT is marked as 0%.
If you add a customer without VAT number and the customer is located in an EU country other than Estonia, then 20% VAT will be added to the invoice.
Xolo manages any VAT obligations related to your business conducted via Xolo Go.