Puerto Rico
Select Puerto Rico as the destination at checkout. The parcel is carried as domestic mail, but the rate is quoted live for the island and priced on its own lane, so the $30 free-standard rule does not apply. Checkout shows a standard and an express option with their prices and estimated arrival windows.
You will not see the word international anywhere in that flow, because Puerto Rico is the United States. Only the pricing lane differs.
APO, FPO, and DPO
Military and diplomatic addresses are entered as a US address. Use the unit or box line as the street, APO, FPO, or DPO as the city, AA, AE, or AP as the state, and the military ZIP code. Checkout accepts these codes, and the label carries the customs declaration that military mail requires even though it ships domestically.
What to expect on timing
Both destinations show an estimated arrival window at checkout like any other address. Military mail in particular can spend additional time in the military postal system after the carrier hands it off, so choose a window with room to spare for a date-sensitive gift.