Can you help me with Events + please

I'm going to go through the customer journey on iPhone 7, so I'm not logged in or anything, so I go to the event page:

https://www.***********cosmeticsrugby.co.uk/events/2018/01/nutrition-event-raising-funds-for-cancer-research-uk/

If I click on I'm attending, it does absolutely nothing. Now if I do the same on my MacBook, also not logged in, I click on I'm attending and it brings up the log-in with facebook button which is great, and the button works. However, its cropped off and looks like this....
http://take.ms/60L55