Design certificate of authenticity for fine art

I'm an artist and need a design for the certificates of authenticity ('COA') I give to the collectors that buy my art. You can see my art on instagram (simonetta.harding.art). I already have a logo designed that can be used for this. The COA will be printed by MOO and needs to fit into their template: https://www.moo.com/uk/design-templates/flyers/?finishingOption=square_corners&origPaperType=matte&paperType=matte&productType=flyer_a4