It is not possible at the moment to take out additional insurance with hvv switch. When you book a SIXT share car using the hvv switch app, the only current option is to book with the standard liability limit. Details about this standard liability limit can be found in the SIXT share tarifs.
Good to know: Only the functionalities of connected partner services offered in the app can be booked through the hvv switch mobility platform. You cannot make use of or book any special offers, packages or vouchers available with mobility partners while using the app.