What is the burden of proving proper service to a party who has denied service?

As set forth above, the burden of proving that personal jurisdiction was acquired rests with the petitioner. [If] the process server is living and available to testify, [a] defendant's sworn denial of proper service renders the affidavit of service non-conclusive and shifts the burden of proof to plaintiff to substantiate the allegation of personal service therein. Under such circumstances, a hearing on the question of whether the affidavit of service establishes proper service requires the affiant must be made available for cross-examination by the party denying receipt (Anton v. Amato, 101 A.D.2d 810 [2d Dept 1984] ).