feat(api): Invalid ID error message

src/api/src/main.py

@@ -63,6 +63,7 @@ async def handle_download(
     else:
         cookies = None
 
+    try:
         match mode:
             case DownloadMode.story:
                 story_id = download_id
@@ -99,6 +100,13 @@ async def handle_download(
             },
         )
 
+    except KeyError:
+        # Invalid ID
+        return HTMLResponse(
+            status_code=404,
+            content='The story you tried to download does not exist or has been deleted. Support is available on the <a href="https://discord.gg/P9RHC4KCwd" target="_blank">Discord</a>',
+        )
+
 
 app.mount("/", StaticFiles(directory=BUILD_PATH), "static")