As several thousands of applications have been submitted so far and your issue remains it looks like it’s a temporary issue with your internet browser.
As a first step please try to apply from a different type of device (smartphone, tablet), a different up-to-date internet browser, and if possible, from a different network preferably not on WiFi connection.
Please also check the settings of your antivirus software and the browser add-ons (e.g. blocking advertisements etc.)
If you still haven't submitted the application successfully, please also follow the steps below:
- Close your internet browser
- Reopen the internet browser or choose another one and make sure you are using its most recent version
- Clear your browser cache (more information on how to do that can be found here: http://www.refreshyourcache.com/en/home/)
- Enter the ticket portal at https://tickets.uefa.com/uclf
- Submit an application