Generally this will be related to one of the following:
1. Sometimes browsers and devices get into a weird state. In this case, restarting the device usually fixes the problem.
2. Older devices and browsers sometimes have difficulty recognizing newer security certificates, which causes this issue. See our recommended devices/browsers.
3. Some security plugins may prevent the game from loading. Let us know which plugins you have and we'll help you configure them to make our game work.