Phantom forces moderation has a way to join via URL, however, it requires users to install a fairly simple script via greasemonkey or tampermonkey. That’s the only way you’ll be able to do it. Does not work with VIP servers unless you have the invite code
We add ?instance= parameter to the url, and the script gets that instance ID and uses roblox’s already available libraries on the website to launch the game. You’ll have to figure out the code, but it’s along the lines of using Roblox.GameLauncher.joinGameInstance(placeid, jobid); in the script