I'm trying to add mekanism osmium and tin but everytime i start the game i get a error saying that the osmium ore does not exist.
I have added

mekanism_osmium_ore.txt
mekanism_tin_ore.txt
oreOsmium.txt
oreTin.txt

with the json extention insted of txt in the ore_stone_variants_mods config folder.
and added them to the config file

ore_stone_variants.txt

i have not done the worldgen file yet. Have i missed something?

If i remove the
mekanism_osmium_ore
mekanism_tin_ore
from the config file the game starts but no new ores are added to jei

What's the exact file structure you're using? These files were supposed to be named "OreProperties.json" and "RecipeProperties.json" respectively and placed inside of a folder or zip named "mekanism_X_ore" prior to version 5.0. If so, then that may be the issue. If not, then there's a bug that I need to look into before the next update.

it was \config\ore_stone_variants_mods/mekanism_X_ore.json but i will try the other way

--edit--
that was it. the instrucktions where a bit confusing

--edit2--
Ores are added but the smelting recipe is emty. as in you smelt the ore to nothing

--edit3--
Mamanged to fix it it should have been
"result" : "mekanism:ingot",
"resultMeta" : 1,