We distinguish among three different cases:

Your business is located in Germany: we automatically charge you 19% in sales tax. This will be reimbursed by the tax office as part of your VAT refund if you are subject to VAT as a provider. 

Your business is located in the EU but not in Germany: if you are liable for VAT, you can enter your VAT ID / Tax ID in bookingkit under Settings -> Company Data. In this case, the so-called "reverse charge" method applies and bookingkit will not charge you sales tax. 

Your business is located outside of the EU: you do not need to take any further action and invoices received from bookingkit are automatically issued without VAT.