Hey @Kristina406 I hope you are well!
I had the same issue accepting co-hosting invites last week, but not for an experience.
I accepted the invite and it looked like the listing downloaded to my account but it didn't- and then when i tried to accept it again I got the error message.
I asked the person sending the invite to send the invite again, and it worked on the third try- if that's not working for you then I don't know what else you could try- maybe an experience host might pop up to help you, but it's mainly homes hosts that are active here.
Best wishes
Paul.