I once booked a plane ticket from my home town airport to another country. The purchase notification said something like "PVA" instead of "POV". I looked it up and turned out, the newly built airport that had this exact code was about to open. In a week or so, so I assumed that I'm indeed flying from the new one and forgot about it. The purchase was made through a booking aggregator similar to Expedia.
On the day of travel I took a taxi to the new airport, which is 40 km outside the city. The taxi driver couldn't care less about where I was going. Upon arrival, there was much fewer people than I expected but I shrugged it off. At the entrance though I was asked where I was going and if I was an employee. Apparently the new airport was still closed and my fight was from the old, still functioning one. The one with the code not shown in the ticket purchase receipts.
Panicking since it was only about an hour until departure, I took a taxi back to the old airport, which was a desperate 40-50 minute drive to only realize the plane had already left.
I was flying abroad, with a connection the next morning, about 10 hours later. So I thought that the problem could be solved by just arriving there by any other flight, which I booked almost immediately. However, the airline representative (yes, there was a human to speak to that I could reach easily by phone) told me that a no-show for any segment of the flight invalidates all subsequent ones. There was no way I could convince her that it wasn't my fault. Perhaps there was a rigid process in place that disallowed her from helping, even though I'd make it to the second flight on time.
I ended up buying 2 new tickets, of course more expensive and less convenient ones. This taught me an important and rather expensive lesson on why connected flights with a single airline are sometimes the worst.
Funnily enough, I was bitten by this rule one more time when I didn't show to a flight in to the country due to visa issues (it was covid time) and wasn't allowed on the flight out of it because I didn't show up to the 1st flight, the flights being 1 week apart - but booked in one go.
As to the previous situation, I managed to get compensated by the airline (not even the intermediary!) about a year later after posting a huge rant on Facebook and getting their attention to the situation.