All he needs is a postage stamp. He can write a letter back with a piece of paper and a pen without any money on his books, as long as he has a stamp to mail it.
If he has nothing at all in his account, most facilities have an indigent inmate program that provides basic supplies including postage stamps to inmates who have had a zero balance for an extended period. The amount is limited, typically enough for a small number of stamps, but it means even an inmate with no money can still send outgoing mail.
The InmateAid letter service handles your outgoing mail through their office, so your home address stays private. For his response, he just writes back the old-fashioned way, paper and stamp, addressed to wherever you have directed him to send it.
Thank you for trying AMP!
You got lucky! We have no ad to show to you!