When booking nextbike, TIER or Voi, an authorization of the registered payment method of 1€ is made. For SHARE NOW bookings the authorization is 20€. This authorization amount will not be debited but blocked for a period of time. The payment method is only charged if the trip is actually priced and finished and of course only to the amount corresponding to the duration of the booking.
Authorization is a security feature that checks the availability of the stored payment method.