, the undersigned, as the Administrator of the XXXXX, attest 1) that YYYY has paid the full registration fee for the XXXXX, and 2) that this fee is mandatory for having the accepted papers published.
The administrator CAN attest to the payment being made, but really can't attest that the fee is mandatory. He can attest that he has informed the applicant that the fee is mandatory but even that is confusing and could not be verified. I think you need a separate line for the applicant to sign showing that he understands the fee is mandatory in order for the papers to be published.
The signature of the undersigned and the applicant should be listed below, and MUST be dated.