What does amazon actually need before you can list supplements?

Check the ingredients against Amazon's restricted products list before you formulate, not after. Some ingredients can't be sold there at all no matter how good the testing is, and some supplement types need category approval first. Finding that out with inventory already made is expensive.

On the US marketplace the big one is testing. Amazon wants dietary supplements tested and verified by one of its approved third-party testing companies before the listing goes live, and that's per product, so budget for it. Beyond that: a label that meets FDA supplement labeling rules (supplement facts panel, the right disclaimers if you make structure/function claims), clear photos of every side of the label that match what's in the listing, and a manufacturer working under cGMP. Your listing copy can't make disease claims either, that gets supplements pulled constantly. Read the dietary supplements policy page in Seller Central before you order inventory. The rules change and the testing step alone can take weeks.