Situations occur with bookings where for whatever reason we need to add something to the booking. Currently this is an entirely manual process requiring multiple exchanges of emails or a guest calling and talking with someone to get something added to their booking. We see this a lot with the channels that do not support things like pet fees or optional fees (mid stay cleanings, early checkins or late checkouts, hot tub fees, pool heat fees, EV chargers, etc etc etc....), and recently we are seeing things like post stay additions - housekeeper tips.
I would like to suggest that there be a Guest Booking Portal or some kind... A guest could go to a login page enter the ORB and another piece of information like a phone or last name. (to confirm who they are) The page would then show their booking information and give them options to add surcharges. Invoicing would be done similar to if they had created a booking on the website...with payment rules being followed as defined for the property/booking. In the case of OTAs we currently have to "disconnect" them from the OTA to add charges... not sure why this is even a requirement the underlying data should know where it came from... So for an AirBnB transaction where the guest receives my email that the hot tub wasnt included on their booking (see my previous Feature Reqest for tags on surcharges) I could add a link to the online Guest Booking Portal... guest could click on it... authenticate... click on the surcharge or charges they want to add... checkout... enter their credit card information to pay. If a guest then cancels on AirBnB any paid surcharges would be refunded to the credit card they were charged on.