You also need tree resin (no idea what it's called in the English version) which you can get from fir trees.

You'll need resin and check that they aren't just immediately drying your hides before they can turn it into leather. I usually turn off my skin drying racks when i need leather and turn off my tanner when i need dry skins.

Yeah I set the dry skins to around 10-15 so that any more skins coming in are turned into leather. You also need "tanning" collected from trees to make one leather on the tanner. You can set a work place on trees to collect tanning :)

Hey thanks everybody my issue was resolved it was just me not understanding i needed the tannin as well