I just downloaded the sample file from @Gladiator_FX95.
And followed @UE_FlavienP advice to change
rel material: binding = </root/mtl/Material__25>
to
rel material: binding = </root/mtl/Material__25/Materials/USD_Default>
I also changed the texture path of the three files that are included at the carpaint.mtlx
Afterwards I go in Unreal to Virtual Production > USD Stage → Render Context → mtlx
Loading \usd_mtx\usd\test_usd_carpaint.usd
But I don’t see any material:
Version: 5.3.1-28051148+++UE5+Release-5.3