If an artwork is accompanied by a Certificate of Authenticity, you can note this by checking the “Certificate of Authenticity” box in CMS. You will then be asked to check whether the COA is from the authorized authenticating body or issued by the gallery.
A common mistake when listing a work is to state that it is accompanied by a Certificate of Authenticity from the authenticating body, when in fact the accompanying document is a gallery-issued COA, original invoice, or other documentation.

Allowed :

A certificate of authenticity (COA) is a document that verifies the artwork’s authenticity. A COA from an authorized authenticating body is typically from the artist, the printmaker who collaborated with the artist on the work, or, for secondary market works, authorized estates or foundations. A gallery may also issue a COA to certify authenticity.

COAs typically include the name of the artist, the details (title, date, medium, dimensions) of the work in question, and whenever possible an image of the work. COAs are also typically signed by the issuing party.