3D Max quick ID map Bake into Substance painter

Select some colors export the fbx into substance select bake id by vertex color dont thick "use low poly mesh as high" if your high poly has the color changed just select the high poly mesh and bake the same way.

[@Mike930806]

So this is after you done UV unrap on your HP correct and add colours ids to your mesh and no material ids on them or?

[@Damian_h]

only low poly has UV Maps. Then u bake all the details from high poly into the islands UV from the low poly. No material ID needed but thats other way u can do it too by mat ID just remember to choose the correct Bake in substance(material ID) instead of vertex color. Just select the color areas u want in ur high poly then bake it into ur low.