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[Jeelkumar-patel]

Is the utilization of this API complimentary, or does it entail usage constraints, such as a predefined limit on the number of requests, beyond which access may be restricted, necessitating a subscription or payment for continued usage?

[JoNilsson]

Is the utilization of this API complimentary, or does it entail usage constraints, such as a predefined limit on the number of requests, beyond which access may be restricted, necessitating a subscription or payment for continued usage?

You have to establish a Developer Account with the USPS, put a CC on file (assume for identity / KYC purposes) and jump through a few other hoops.

Once you get a UserID, you can hit the OAuth2 API and request auth tokens. Then you can use your UserID to make requests against the Address API. You can issue 60 request per-hour. There is no costs associated with the use of this public API.

All the DOCS are here: https://developer.usps.com/