The extra fee you received is the Service Fee and this fee is the service charge for using the Ticketing platform.
This information is referring on the fee breakdown page before you complete your transaction. A legal receipt is issued for this amount which you can find by following the link with the detailed information sent to your email.
Using your Viva.com personal account there is no additional charge.
Important note: It is at the discretion of the organizer whether all payment methods will be available.
This means that the cash option, acceptance of all cards or the option to pay with a Viva.com account may not be available.