You set sv_loadingurl, and players still land on the default background. It's annoying, and it's almost always one of seven things. Work through them in order. The first three account for most of the cases I've ever had to chase down.
1. The URL has no quotes around it
If your URL contains ?, & or spaces and isn't wrapped in double quotes, the console reads only part of it. Sometimes it skips the whole line.
sv_loadingurl "https://example.com/loading?map=%m"2. The line is in the wrong file
The variable must be executed by the SERVER. Put it in garrysmod/cfg/server.cfg on the server's filesystem, which you reach through your hosting panel's file manager. Not your local client cfg. And not some gamemode config that never actually runs.
3. The server wasn't fully restarted
server.cfg is read at startup. A map change or exec server.cfg sometimes works, but the reliable test is a full stop and start from your panel. Then type sv_loadingurl into the server console to check. It should print your URL back.
4. Your own client cached the old screen
GMod's embedded browser caches pages hard. If YOU still see the old screen but new players see the new one, that's your cache, not the server. Test from another account or machine before you go changing anything else. Many server owners learn this the hard way.
5. The page renders black or blank in-game
The screen applies but shows nothing? GMod's browser is Chromium under the hood, but it's stricter than the Chrome on your desktop:
- The page blocks embedding or requires interaction before rendering.
- Mixed content: an https page pulling http images or audio. Those assets get blocked.
- A JavaScript error early in the page kills rendering. Open the URL in desktop Chrome and watch the console.
- HTML5 video. The in-game browser won't play it, so a page that leans on a video background can come up black.
6. Free image hosts died
Screens built on hotlinked imgur or ibb images tend to break without warning. The host blocks hotlinking or deletes the file, and your background turns into a black rectangle. Host your assets somewhere they'll stick around, or use a service that stores them for you. Lumescreen serves uploads from its own storage for exactly this reason.
7. The hosting panel overrides your cfg
Some hosts regenerate server.cfg from panel settings on every boot, which quietly overwrites your manual edits. If your line keeps vanishing after restarts, look for a 'loading URL' field in the panel itself, or a documented way to turn off the cfg regeneration. Pterodactyl-based panels are common offenders here.