I went to your calendar and in the available stretches the system is warning me that there is a 14-night minimum, so it looks like you've set a minimum and it's working. I couldn't see a problem.
Hi there @Gabriella698, I was wondering whether you have seen the reply from @Shelley159? I seem to get a similar warning as well checking your calendar.
If you found Shelley's answer helpful, please do feel free to mark her answer as a "Top Answer" 😊
I called Airbnb and had to go to my Calendar, then Settings and had to renove any Custom Trip Lengths which had been mysteriously recorded and which allowed for short stays.