First make sure that your buyer has a registered VAT number and add it to your customer data.
Both the buyer's and the seller's VAT numbers need to be on the invoice. You can easily check the buyer's VAT number on the European Commission's online service. You can add your own VAT number at My account -> Company contact information.
 
Note:
Other than within the EU there are no standardized regulations on VAT requirements for third countries. Some countries outside the European Economic Area also apply the reverse – charge system, such as Switzerland. However, as there are differences between countries, always inform yourself about the fiscal regulations of the country before you sell your services (information can be at German Chambers of Commerce Abroad).

Invoice standards differ from country to country and there are no German/Austrian requirements for invoice templates. However, in order to avoid misunderstandings we recommend to add “nicht im Inland steuerbare Leistung“ to your invoice footer text. Don’t forget to set out a separate advance return for tax on the sales. However, it is not required to submit a recapitulative statement (as required by the reverse charge system).
 
Creating an invoice for sales of services outside EU:
1. Go to the Invoices tab and click on Create invoice on the right.
2. On the right side of the editor you see the invoicing settings panel. Select Sales of services outside EU as invoice type.
3. If needed, you can also choose another Currency and Invoicing language.

Zervant will automatically remove the VAT from the invoice. Remember to add "Nicht im Inland steuerbare Leistung" to the invoice footnote.

Attention! If you choose another currency and add products/services on the invoice directly from your registry, you will need to manually recalculate the price of the product/service according to the new currency.