There are two conditions you cannot make a reservation. One is that the payment is already completed and the other is that the payment has not been completed yet.
1. The payment has not been completed yet
If a payment has not been completed yet and you cannot book facilities you need to book because these are busy or closed, guides and guests need to make an alternative plan. In this case, tell guests as soon as you find out that you cannot make a reservation for the facilities/activities and cannot go. Although it is bad news, you would better tell it to guests as soon as possible. If the guide has already sent an offer, the guides or guests cancels the offer, talks over again and send a new offer including new itinerary to guests.
2. Already the payment is completed
In the case that guests already make a settlement despite you cannot make a reservation of facilities/activities, there are many cases that the trip included the facility fee and payment is already completed. In this case, tell the guests as soon as it turns out. Although it is bad news, you would better tell it to guests as soon as possible. Then discuss what to do about the trip with the guests and decide whether to search for an alternative facility, to do other things, or to cancel the trip itself.
If fees change, there are several solutions. First, cancel the trip from the guide's side once, send a new offer and the guests make a settlement again. Second, directly refund the facility's fee to the guest on the appointed day. Regarding the second, TOMODACHI GUIDE cannot be concerned because the refund does not pass through the system.
In any cases, if guides cannot make reservations of facilities you needed to book, let the guest know immediately, discuss with them and decide what to do.