Here is the NJ service of process rules that apply. Notice the following language under Rule 4:4-3:
If personal service cannot be effected after a reasonable and good faith attempt, which shall be described with specificity in the proof of service required by R. 4:4-7, service may be made by mailing a copy of the summons and complaint by registered or certified mail, return receipt requested, to the usual place of abode of the defendant or a person authorized by rule of law to accept service for the defendant or, with postal instructions to deliver to addressee only, to defendant's place of business or employment. If the addressee refuses to claim or accept delivery of registered or certified mail, service may be made by ordinary mail addressed to the defendant's usual place of abode. The party making service may, at the party's option, make service simultaneously by registered or certified mail and ordinary mail, and if the addressee refuses to claim or accept delivery of registered mail and if the ordinary mailing is not returned, the simultaneous mailing shall constitute effective service. Mail may be addressed to a post office box in lieu of a street address only as provided by R. 1:5-2. Return of service shall be made as provided by R. 4:4-7.
So give these other options a try.
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