You are trying to pick up a cancellation for the summer months for restaurants that are so popular that they were probably booked up on the 180th day before your trip. It can be done, but it takes effort, perseverance and luck. You will need to have the luck to be checking pretty close to right after someone cancels. You definitely want to use the app. You want to be checking multiple times a day every day- and I'm talking as much as you can. I have done it before for A&E FP+ (in the height of the frenzy) and for ADRs when we wanted to change nights or restaurants- but it basically took me leaving the window open while I sat at my computer at work and checking over and over when I got the chance. Keep trying right up until the day you want to eat there- cancellations do happen! Good luck!!!