Hello Pablo Veliz.
Thanks for reaching out. The GET https://graph.microsoft.com/v1.0/solutions/bookingBusinesses/{Id}/appointments API call will only work for scheduling mailboxes.
To find a list of addresses for the booking calendar use the following API call https://graph.microsoft.com/v1.0/solutions/bookingBusinesses/.
Please refer to the below articles for more information on Microsoft Bookings:
Microsoft Bookings Behind the scenes
Using scripts for Microsoft Bookings calendar and mailbox
Thanks.