Hello PoPi,
Please clear your browser's cache or try with a different browser. 

If you're using a VPN, make sure to deactivate it before starting the subscription process. Almost all servers a VPN provider has are marked as "known proxies" which causes sites like worldpay.com and online banking sites to refuse the connection!

In case this does not solve the problem please read the FAQs 

https://www.flyordie.com/games/help/support/contents.html

 
before contacting FlyOrDie's technical support 

https://games.flyordie.com/s/contactSupport.html?portal=flyordie_com&lang=en

  
( Please give them a few days to get back to you.)

Kind regards,
John