Product Variations

I was able to get the color variations listed on the products, however I have added the size features and I'm unable to add them as well to the products? Can I get more instructions on how to do this? I did exactly what I did on the color variations except I clicked variations as one product instead of variations of separate products when I added the size feature. The size features show up on the features but when I go to add it as a variation it doesn't give me the option. What am I doing wrong?

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