Vehicle doesn't appear in-game — double check the resource actually started without errors in your server console, and that any required dependency resources are also running.
Resource won't start / errors on start — this is usually a license check failing (see "How license keys work") or a missing dependency. Check the console output for the specific error before contacting Support, since it usually tells you exactly what's wrong.
Streaming assets not loading — confirm the stream folder is registered correctly in the resource's fxmanifest.lua and that file names match exactly, including case.