Shopify Store shows that product is sold out even though there is stock

[Hejlos]

Hello,
I am new to this and I have just made a Shopify dropshipping store using Zendrop as a supplier. The problem is that when you go to the product page, you can add the product to cart but as soon as you select a variant it says "Sold Out". Does anyone know why this is happening?

Link: https://969261.myshopify.com/products/portafrost-waist-fan
I do not have Shopify payments set up yet if that has anything to do with it.

[Hejlos · Accepted solution]

Never mind it works now I just used outdated code so I updated that and now it works fine.

[vince7]

I have the same problem but how do you update the code

[Ca18]

I am facing same problem 

How do I solve this