Error 18821 — Return policy attribute invalid

Your return policy fields (return_window, restocking_fee, etc.) don't match Amazon's accepted format or violate Amazon's marketplace return rules.

Amazon enforces marketplace-wide return rules — typically a minimum 30-day return window. Submitting shorter windows or unsupported fee structures triggers this.

1. Set return_window to at least 30 days (Amazon's marketplace minimum).
2. Restocking fees must comply with Amazon's policy — typically max 20%.
3. Use Amazon's pre-populated return policies via Seller Central → Settings → Return Settings.

• Setting 14-day return windows — below Amazon's minimum
• Restocking fees over 20% — flagged as policy violation