To summarize, the key aspects required by Amazon are:
1. A Certificate of Analysis (CoA) from an ISO/IEC 17025 accredited laboratory (in-house or third party) for each dietary supplement you are applying to list OR product enrollment in an Independent Quality Certification Program, such as NSF International Sport, BSCG, Informed-Choice/Informed-Sport, or active participants of USP Dietary Supplement Verification Program
2. A Letter of Guarantee from the brand owner of the product that guarantees compliance with current Good Manufacturing Practices (21 CFR Part 111); assurances that the products only contains lawful and safe ingredients (as defined in section 402 (f) of the FD&C Act); and that labels are accurate.