You cannot mail US goods to military, government, or contractors who have an APO in which that mailed product will be delivered to a local national, a German in this instance. It is against the Status of Forces Agreement (SOFA) due to taxation and use of NATO mailing services to avoid paying import and duty of products received from the US. The person who owns the APO could face stiff fines, penalties, and loss of a security clearance and job if they are held culpable for such an action.
Ciao,
Ciao,