If you do not find any solution then I request you to reinstall the game app. To do this you will lose the stored boosters but your problem may be solved.
@Lolomw try using a different browser than Safari see if you still get same problem. safari you can try clearing the cache / history and then restarting.
@Freddy_Falkner thanks for the advice. I managed to clear the history and got a step further but now it says this. which is not true cause the internet and my 4G works very well:
I also tried Chrome on desktop and it still says this:
Hey thanks for sending this but the app was never installed on my phone or Facebook. I downloaded Candy Crush saga this week and never even had the chance to connect to my Facebook so I can’t find it in my games.
@Lolomw you downloaded on to what device is this an apple pc or ipad . have you tried connecting to facebook first in a browser and then try logging into game. may find if app try uninstalling and reinstalling