The APO is usually just a temporary address used as long as he's staying in Germany. Use his real address in the US to establish domicile along with some other evidence like government orders, real estade paid taxes, utiliy bills, rental agreement, rental fees or whatever shows that he is still maintainig a domicile in the US. This along with a short cover letter worked perfectly for us.
Here is our cover page:
Mikey Mouse
CMR 999, Box 999
APO AE 12345
September 23, 2023
National Visa Center
RE: I-864EZ, Affidavit of Support
NVC Case No: XXXXXXXXXXXXXXXX
Applicant: Mikey Mouse
Beneficiary: Minni Mouse
To Whom It May Concern:
I am currently stationed in Germany under Army Permanent Change of Station orders. I have maintained my primary residence on Mars, Solar System, where we will live after my spouse’s immigration is complete or at the completion of my Army tour.
I am submitting additional documents supporting my domicile claim, temporary nature of my tour in Germany and intention to live permanently in the United States. Attached please find the following documents:
Government Orders/Approved Tour Extension
Rental Management Lease Agreement
Real Estate 2022 paid taxes
If you have any questions or concerns, please call me at (555) 555-5555. Thank you for the time taken in this case.
Sincerely,
Mikey Mouse