Common vignette mistakes that are easy to avoid
The small errors, a wrong date, a wrong vehicle class, that cause most vignette problems.
Most vignette problems don't come from skipping the purchase altogether. They come from small errors in how the vignette was bought, ones that are easy to make and just as easy to catch if you know to look for them.
A mistyped licence plate
Since e-vignettes are tied to your plate number rather than a physical sticker, the system checks that number specifically. A single mistyped character, an easily confused letter and number, or a missed hyphen or space means the system won't recognize your car as covered, even though you paid for a valid vignette. This is the single most common mistake, and it's also the easiest to avoid: double-check the plate against the vehicle itself, not against what you remember from the rental paperwork, before you complete the purchase.
A start date that doesn't match your actual crossing
It's tempting to buy your vignette in advance and pick a start date based on when you're planning to leave, but plans shift. If your departure gets delayed by a day and your vignette's active period has already started, you're burning validity time you won't get back. Where the option exists, it's worth setting the start date closer to your actual border crossing rather than the date you happened to be booking the trip.
Buying for the wrong vehicle class
A vignette bought for a standard passenger car won't cover a vehicle that falls into a heavier weight class, and the reverse means paying more than you needed to. This comes up most often with rental vans, campers, or anything modified from its original registration weight. Checking the vehicle's registered class before buying, rather than assuming based on how it looks, avoids both problems.
Assuming one country's rules carry over to the next
A vignette valid in Austria says nothing about Slovenia, Switzerland or anywhere else, even on the same trip. Crossing a border resets everything: you need a separate vignette for each vignette country you drive through, and a completely different approach for countries that charge tolls by distance instead. Treating each border as its own checklist item, rather than assuming continuity, is the most reliable way to avoid a gap in coverage.
None of these mistakes involve trying to avoid payment. They're all about details that are easy to get right once you know to check them, and considerably more expensive to get wrong at a checkpoint.