If you need to send money digitally without visiting a physical location, consider these online-only services: Sending Money Orders - USPS
Since you can't buy them online, here is the standard process for getting one at the Post Office: buy postal money order online
You cannot buy a physical USPS postal money order online. You must purchase them in person at a Post Office location using cash or a debit card. How to Get a Money Order If you need to send money digitally without
: Bring cash or a debit card; credit cards and personal checks are not accepted. buy postal money order online