In contrast to sticker vignettes/paper vignettes, the digital vignette does not need to be affixed to the windscreen. Instead, you will receive a control section (Voucher) to the e-mail address you have provided a few minutes after successfully ordering. It is important to carry this control slip with you during your journey. 

On the toll road, your licence plate number is automatically recorded and compared with the data you have stored with the toll operator ASFINAG. If the digital vignette has not been ordered for your vehicle or has not been registered correctly, high penalties may be incurred. 

You can find more information on how to enter your licence plate number correctly here.