@Emilie
Sometimes the Airbnb BOTs automatically issue a warning notification on a message/booking request because they suspect someone is trying to exchange contact details off platform.
It happened to me just yesterday when a guest sent a booking request. She was not trying to pay off platform, but she was worried about her profile photo not being okay (not sure why she just didn't change the photo) and directed me to her Facebook. This guest is not a scammer, she's just inexperienced and doesn't know how the system works.
So, in order to respond, you are given two options, either to report or to ignore. I chose ignore and I was using Safari at the time. I think what @Doug163 means is that this option did not appear on Chrome and therefore you could not continue with the booking process. Of course, the same option should appear on Chrome or Safari so it's obviously a glitch.