When under private signature they must be attested by 2 witnesses, and cannot be received by the Registrar unless they are accompanied by an affidavit of one of such witnesses sworn to before one of the functionaries mentioned in articles 2022, 2023 and 2024,as the case requires, and establishing that the money has been paid in whole or in part, and that such acquittance, certificate of discharge, or consent to the cancelling was signed in the presence of such witnesses by the party granting it.