Invoice requirements are stated in the VAT legislation and very important for an entrepreneur to take into account. Among these requirements is the correct mentioning of the VAT amount. Have you mentioned the VAT amount correctly in your invoice?
The VAT amount is an amount in the euro currency. If you then for some reason issue and invoice in another currency, make sure that you have somewhere on the invoice the euro equivalent of the VAT amount mentioned.
Does this happen often? Not really, most invoices within the EU are send at 0%. But to private individuals the invoice does need to contain VAT. However, if you do business with private individuals, there is no obligation to issue an invoice. If you do issue an invoice to a private individual that is not meeting the VAT invoice requirements, you can get a penalty for issuing a wrong invoice, whereas you have no obligation to send an invoice in the first place.