Fix #3: Check Roblox server status. Sometimes, a Roblox game may not launch or return an error like the HTTP 503 service unavailable when you try to open it because of an on-going server trouble.

Check the firewall settings and allow Roblox application to run as the firewall may have blocked the software. This solution seems to be the most effective based on players’ comments.

With Roblox available on many formats, here's everything you need to know about the game, including tips on how to play safely online.