You are listing against an existing ASIN, however Amazon have restricted marketplace sellers from selling against this ASIN with particular product conditions. For example Amazon is only permitting listing against the ASIN for used items and the item you are selling is a new item. Or Amazon is gating this entire brand to only approved sellers
1. Use the Find barcode wizard to match against a different ASIN (a different existing Amazon listing).
2. Ensure the condition of your product is specified correctly.
3. Go to Seller Central and request approval to sell this item, which will remove the gating.