Just to warn you guys…webcal.fi, a free online calendar service, switched to paid mode. If your phone systems are controlled by this online calendar, you have to use ownCloud/nextCloud solutions instead.
The owner of webcal.fi started to create random events (containing the info of the new service) in all active calendars, which gives you a weird behavior of your phone systems.
e.g. if you used the holiday calendar to switch your phone system into the we-are-closed mode…you will be closed every few days in the future
And here is the solution: