In some instances, the customer can make a mistake within the address they type in the checkout process. There might be a typo or the state or zip-code might be wrong.
The video below demonstrates the USPS address validation system, which goes in and checks the address given by a customer for you.
As of May 2023, in order to toggle the USPS Address validation feature on/off, you must visit wp2print, >settings, >Address Validation