Users of Facebook, Instagram, WhatsApp and Messenger are currently experiencing problems. The websites of the services are not working, something that is also shown by downdetector.

Users of Facebook, Instagram, WhatsApp and Messenger are currently experiencing problems. The websites of the services are not working, something that is also shown by downdetector.

"Unable to access this site" is the message that visitors to the above pages have been seeing for some time.

There does not appear to be any official update at this time, but all pages displaying Facebook service status display downtime.
The problem seems to exist not only in Greece, but also in other countries around the world. We are waiting for developments, or some official announcement, that justifies the problem.
We're aware that some people are having trouble accessing our apps and products. We're working to get things back to normal as quickly as possible, and we apologize for any inconvenience.
— Meta (@Meta) October 4, 2021
Note that there was no downtime warning, which means that it was not planned by the company.
The company after the celebration published the above tweet.