Hi @Anonymous,
@Ed-and-Hugh0 is correct! Once you have a confirmed Reservation with a Guest you should receive email and phone contact options to reach them directly as needed. That'll allow you to send any additional information (attachments etc) to Guests as needed.
Do your best to keep things on platform where you can though as it ensures Airbnb can 'see' what is going on should there be a hiccup.
Cheers,
Paul
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