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by andymcsherry 1551 days ago
If you use the USPS API, it gives you a specific message if it's a multi-unit address:

Default address: The address you entered was found but more information is needed (such as an apartment, suite, or box number) to match to a specific address.

Verify API, page 11

https://www.usps.com/business/web-tools-apis/general-api-dev...