I am still having this issue. I copied a working Flow before I started making changes.
I looked at the link that @Darren_Carr shared. It did say you have to be an Admin on the Bookings and that only 5 flows can be made for any calendar. I ensured that there are only two flows using that calendar.
I'm an admin on the Bookings calendar - I actually created it. Here's what I'm seeing. The Flow is not being triggered. When I open it from the list of My Flows, I get this error:
I can't figure alt text - the error banner reads: Ther is a problem that needs to be fixed to trigger this flow. To see more details, open flow checker.
When I open the Flow Checker, I get this
There's a problem with this flow's trigger. Details: it hasn't been triggered successfully in the last 28 days.. How to fix it. To see this problem and fix it, go to the trigger.
When I click that link, I get a totally white area to the right of the menu panel. When I refresh, I get the flow failure screen, showing the trigger failed.
The run details

So, I look at the trigger block

Here's the offending raw input:

On the right, the resources to help solve this ...

I have not tried to sign out and reauthenticate - that's my next step.