What you will end up with
A folder in your server's resources/ directory, one line in server.cfg, and a car that spawns with textures, proper physics and a real display name. Total time for one car is about five minutes; for a pack of twenty it is about twenty minutes because most of that is uploading.
Note
Everything below runs in your browser. Nothing you upload to the Inspector, Optimizer or Pack Builder leaves your computer; the only thing sent to a server is the gta5-mods.com link in step 1.
Step 1: Convert the mod
Open the converter, paste the page link of the vehicle (it looks like gta5-mods.com/vehicles/2015-bmw-i8, not the download button link) and click Convert. In about 30 seconds you get a download button. The zip is a complete FiveM resource: fxmanifest.lua, a data/ folder with the meta files and a stream/ folder with the model and textures. There is also a README inside with the install steps.
Tip:
If the converter says the page could not be fetched, open the link in a new tab to confirm the mod is still public, then try again. Failed attempts do not use up a free conversion.
Step 2: Inspect the resource
Drop the zip you just downloaded into the Resource Inspector. It runs 22 checks and gives the resource a score. Read the red errors first: those are the ones that produce an invisible car or a server error. Each finding tells you the exact file and the exact line to change. With Unlimited you also get the corrected fxmanifest.lua to paste over yours and a per-model table showing which car is missing its _hi model, texture dictionary or handling entry.
Step 3: Fix oversized textures
If the Inspector flagged any file over 16 MB (or several over 8 MB), open the Texture Optimizer and drop the same zip in. Pick 1024 px for interiors and most bodies, 2048 px for liveried show cars. Click Optimize. The tool removes the top mip levels so the smaller version already inside the file becomes the new top; no pixels are re-encoded. Download the optimized .ytd (free) or the whole rebuilt zip (Unlimited) and replace the files in your resource.
Step 4: Build a pack (optional, recommended for 5+ cars)
Once you have several converted resources, drop them all into the Car Pack Builder. Give the pack a name, keep "identical shared assets once" ticked, and click Build. You get one resource with a single manifest and every data_file line, plus a list of conflicts: duplicate spawn names, clashing handling entries, mod kit IDs used twice. Fix the red ones before you ship; the pack is downloadable either way.
Step 5: Install
Copy the resource folder (or the pack folder) into resources/. Add ensure foldername to server.cfg. Restart the server, or run refresh then ensure foldername in the console.
resources/
└── my_carpack/
├── fxmanifest.lua
├── data/…
└── stream/…
server.cfg:
ensure my_carpackStep 6: Spawn and verify
Spawn the car with its spawn name (the <modelName> in vehicles.meta, listed on the Inspector's model table and in the pack README). If it is invisible or black, the invisible car guide walks through the seven causes; nine times out of ten the Inspector already told you which one.
Free vs Unlimited in this workflow
Tip:
Create a free account before you start. Every conversion you make while logged in is kept in My Garage, so you can re-download it after the upstream link expires.