UPC for clothing on amazon

Hey,

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I have a Shopify store in which I sell clothes that I buy from wholesalers.

I want to expand my sales and open an Amazon account, and I know that in order to do so I need to get UPC codes for my clothes.

My main question is, do I need a unique UPC for each variant or can I have the sane UPC for each model?

I’m afraid that a unique UPC will be really hard to update all my inventory.

What does everyone do?

Thank you