(404) Feed error

Hi,

I’ve installed the wp booking calendar and added a Google calendar. To try this, I created a ‘fake’ calendar. This worked fine. Now I wanted to set up the clients calendar (another Google account, another api-key, another calendar-id), but when want to import the Google calendar, I get an error:
The feed could not be found (404). Please ensure your feed URL is correct.

There are no more bookings in the system. I’ve uninstalled the plugin and installed it again, but still it isn’t working.

How can I solve this?