Physical address or P O Box to serve him

My husband refuse or he says he does not have a physical address or mailing address because where he leaves he does not trust getting his mail, plus he does not wantme to find out where he lives. he said to send the papers to his PO box and he will sign it as soon as he gets them. I’m just confused, it is no problem to me to use his PO since this is mutual agreement, and I know he checks his box. I called the court place where I got the papers and one lady said NO, it has to be physical address and he has to receive the certified mail. I was not satisfied with the answer and called another day, a different person told me that yes, i can send it to the POBOx, just have to make sure he checks it,

TO be sure I called USPS and they told me what they do is to put a notification on his box, and he has to go to the front and requested, then sign, and they will send me the card…does anyone know the answer to this is it ok either or? I have my papers ready but I don’t want to go file them and they tellme no, I need physical addr.
Please help!!!