If a tanker spawns instead of the intended vehicle, this is usually an ESX issue related to the vehicle class. You can fix it either by editing the ESX file or adjusting the vehicle class in vehicles.meta.

TL;DR:

Change the vehicle class in vehicles.meta or fix the ESX file.

First Method

1.Open vehicles.meta of the vehicle

Find the vehicle model that is spawning as a tanker. Look for the <vehicleClass> line.

2. Change the Class

Change the class to a different standard class, for example VC_SUV.

3. Restart the server or resource

Restart the server or the resource the vehicle is inside for the changes to take effect.
That's it! Your vehicle should now spawn correctly.

Second Method

The second, more permanent method is fixing the ESX file causing the issue.

1. Open es_extended/client/functions.lua

Find the function ESX.GetVehicleTypeClient or ESX.GetVehicleType and set vehicle class [11] in types as "automobile".

2. Restart the server

Restart the server for the changes to take effect.
That's it! Your vehicle should now spawn correctly.