From google seach:

To become a vendor on the Amazon marketplace, you need to receive an invitation from the retail team. If the retail team are interested in your brand they will make contact, usually through email, although vendors have been approached by Amazon at trade shows and exhibitions. If you don’t receive an invite, you could try and reach out to Amazon via the Contact Us link on Vendor Central. Alternatively, I have heard some brands make contact directly with Vendor Managers via LinkedIn. There is no guarantee this direct approach will work or even get a reply. If your brand makes enough noise in the industry, they should be in touch!

To be invited, you need to be attracting Amazon’s attention. It might be that you are a private label seller with a rapidly growing brand and top-sellers in certain product categories. It might be that you have a brand that has a certain market share or influence in a specific industry, or you could have a wide range of products that Amazon is interested in for selection purposes. A lot depends on the product category and their goal at that point in time.

Amazon predominantly works with manufacturers and brand owners, but can also work with distributors if they have brands that are hard to source and can provide Amazon with adequate margins.