Ok, i fixed it.
I had:
[...]
shopModule:addBuyableItem({'wand of vortex', 'vortex'}, 2190, 500, 'wand of vortex')
[...]
shopModule:addSellableItem({'wand of vortex', 'vortex'}, 2190, 250, 'wand of vortex')
[...]
Solution is simply - i had to add '1' but only to BuyableItem, ex.:
[...]...