You will have to contact your lead vendor to request the “full” certificate. Send the lead vendor the “masked” certificate and they will be able to access the corresponding “full” certificate in their account. Your lead vendor must be storing their Certificates in their TrustedForm account for this to work. If they have allowed their Certificates to expire, they can no longer be accessed.
For a full overview of the concept of 'Masked Certificates' click here.