Often on social networks, you can see posts that the ticket bought for the plane turned out to be invalid and the passenger was simply not allowed on his flight. This situation is called overbooking. It occurs when more plane tickets are bought than seats in the aircraft cabin.
Some air tickets are sold at a good discount, but there is one caveat: they cannot be exchanged or returned in case of emergency. The same applies to certain round-trip tickets. Since sometimes passengers with such tickets do not show up for a flight, airlines sell more tickets for this flight than seats on the plane. Therefore, you may be simply not allowed on board with tickets in hand.
There are two ways to find out about overbooking. The first is to call the airline, the second is to ask about it at the check-in desk. Also, a sign that you are overbooked may be the inability to check in online or the inability to choose your seat and get a boarding pass.
If you encounter overbooking, you need to inform the airline about it. Often, in this case, passengers who had tickets in economy class are seated in business class (if there are empty seats). Another airline may be trying to solve the problem to find those who want to fly on the next flight with various privileges. The third option is the payment of compensation to passengers. It also happens that overbooking occurred due to an unexpected breakdown of the aircraft, due to which you have to fly on a less spacious vessel.