Existing custom URL no longer works

I used to have my game at http://themurderoushornet.forge-vtt.com, and has it there for ~2-3 months, but as of today, that URL no longer works. Instead I get the error:

Error launching game: This game is unavailable while the Game Manager is enabled.
This Game is not currently available.

Checking my game’s config, the URL has been changed to jaybe38-weaselia.forge-vtt.com (following this link works). When I try to update the game’s URL back to my custom URL, it tells me the URL has already been taken (which it has, by me).

This appears to have happened after I used the module manager to update 5 of my modules, but I also installed a custom module today, and I’m not clear enough on the timeline to remember which came first.

Can I get my custom URL back please?

So, this is probably because your game is taken by your server.
So if you change your Servers URL then change the worlds, it should work.

You enabled the Game Manager which makes it one new game (with its own URL) per Foundry world. The old URL is still reserved.
What you can do is disable the game manager, change the ‘Foundry server’ url to something else, then enable the Game Manager, and for the world you want, change its url back to the one you wanted.