This is a base64_url-encoded verifiable presentation of a verifiable credential signing over the cart_mandate and payment_mandate_hashes. For example an sd-jwt-vc would contain:

• An issuer-signed jwt authorizing a 'cnf' claim
• A key-binding jwt with the claims "aud": ... "nonce": ... "sd_hash": hash of the issuer-signed jwt "transaction_data": an array containing the secure hashes of CartMandate and PaymentMandateContents.