How to find the product id

Hello, I found a product to sell on amazon that one seller is selling and I have a slightly different product than the one on Amazon. It’s a generic product with no branding. If I want to sell this product, where do I find the Product ID, and can I just get a barcode from GS1 and start selling it? Do I jus get one barcode from GS1 for 25USD and use it to sell that one particular product unlimited amounts of times? Thank you for answers.