Here are the most common causes of errors when creating a label for an international or US military address.
There are foreign characters in the customer's address
Non-English characters can keep the carrier from recognizing the address. To fix this, click Edit on the Recipient Address field and replace any non-English character with its closest English equivalent. This won't affect delivery, and it'll let you print the label.
The sender/recipient name field is incorrectly formatted or incomplete
USPS returns an error if the sender or recipient information is incomplete, typically: "The sender address must contain a first and last name, or a company name must be added."
On international labels, both the sender and recipient name must follow a strict "first name" and "last name" format, with more than one character in each. These don't have to be actual first and last names, your business name works too. For example, instead of just "Shippo" in the first name field, you could split "Shippo Inc." across both fields.
The US military address is incorrectly formatted or incomplete
APO/FPO/DPO addresses can look unfamiliar and get complex. Every piece of information needs to be on the right line, including box or unit numbers, for USPS to accept it. USPS provides a guide on the correct format for these addresses on their website.
The US military address lists the wrong country, city, or state
US military addresses must list "United States" as the country, with APO, FPO, or DPO as the city, and AP, AE, or AA as the state. These addresses may be physically located in other countries, that's just how US military and diplomatic addresses are formatted.
The US military address is missing a phone number
Phone numbers are required for international shipments and shipments to military addresses. If the Recipient address box keeps popping up and you can't get past Step 1 of label creation, make sure you've entered a phone number for the recipient and saved your changes.
Military box numbers in line 2
A common error happens when the box number ends up in the Street (line 2) field. To fix it, enter the box number into Street (line 1) instead.
For example: