How To Update Inventory Of Variants?

I am trying to update the stock inventory of products that are variants, with a csv import but nothing is getting updated. (product example https://www.loxleyarts.co.uk/art-materials/paint-and-media/childrens-and-craft-paint/loxley-readymix-300ml/)

I ran a csv export of the products, edited the inventory stock numbers in the Quantity column and uploaded the same file (see the attached). Nothing changes.

What am I doing wrong? It must be something simple....

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Apologies, how do I upload a file?

I have uploaded it to wetransfer for now https://we.tl/t-fz6GKH7QWx (1kb)

Thanks!