If you are trying to create a new booking, but you cannot complete it because of a"Not enough capacity" error (even though the room seems to have slots available) please check one of these questions:
1. Is it a private room?
If so, please notice that you cannot have a different guest being added in a private room when you already have a guest occupying the room.
In the example below, the guests Angélica Mattos and Jenifer Cruz belongs to the same booking, and you cannot create a new booking for the guest Laurence Jeskwic for the same room and dates.
2. Is the room available for the total nights?
Sometimes the room is available for some nights but not for all the nights you've chosen within the guest's stay.
In this example below, the guest Danilo Padaratz could stay until the 16th of July in the first slot, and from the 17th - 19th of July in the 3rd slot, right under Jenifer Cruz. But since this is a private room, the guest Danilo cannot stay in the same room of the guests Angélica Mattos and Jenifer Cruz (same reason as example 1)
In case you want to add different bookings and guests to the same room, you may want to change its status from a private to a shared room.
Please refer to this article for a better understanding on how to set room types.