The easy answer is NOT Safari or old, unsupported browsers. Many online applications that have a high degree of user interaction are challenged to work without issues in Safari, and FairSplit.com is no exception.
Please avoid using outdated, unsupported browsers such as Internet Explorer. Google Chrome and Mozilla Firefox are recommended.
Apple devices default to Safari when clicking a link, even if Chrome is open. Open Chrome on your iOS device and then copy and paste the invitation link into the Chrome browser to register, and then each time you go to FairSplit.com to login, open in a specific, non-Safari browser for best results.