edit, or just READ Bill's reply, the one from 2 1/2 years ago that was marked as the solution....

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It's an IRS issue, related to EFIN applications.  Several years ago *they/IRS/EFIN police* stopped allowing PO Boxes.  Yes, it's a pain; I'm in a rural area with NO USPS street delivery so I must use a PO Box.  Clients routinely mail (USPS) things to me at the physical address shown as preparer.

My decision, years ago, was that fighting the IRS *AND* the USPS is a battle I couldn't win.