Sometimes when you are trying to connect an Airbnb account it will fail. This is usually cause for 1 of 3 reasons
A PMS or Channel Manager is already connected to that host
You are logged into multiple Airbnb accounts on your browser
You already connected this host to Channex for another property
Incognito Mode
First thing to try is to open a incognito window in your browser and connect. This makes sure you are not logged into any accounts already. If you still cant connect then it is from reasons 1 or 3
Check if an app is already connected or Channex is connected already
Go to "Account"
Then click in "Privacy & Sharing"
Check if Channex is connected already, if it is the old app then you should remove it.
Under Connected Apps, click on "Remove Access" next to the channel manager connection.
Channex is already connected
If you saw that Channex is the channel manager connected to the host, then it means you have connected it already for another property. You should find that channel and add more properties to the connection.
If you don't know how to find the channel then please ask support to find for you