@Sal1, the main reason AirBnB requires communication to go via the ABB platform is to protect both guests and hosts in case problems arise. AirBnB makes its decisions on the basis of the exchange of messages on the platform (along with what House Rules have been described in the listing, in the event that a host claims damages because house rules have been broken).
In helping to resolve an issue, AirBnB does not take into account any off-platform communication.
One solution to your problem might be to take photos of the information you want to send, and then include these photos in the pictures on your listing.