"Error PB Shipping API: 1021003 Invalid/unsupported GU country Code" when shipping to Guam in SendPro Enterprise

The message "Error PB Shipping API: 1021003 Invalid/unsupported GU country Code" appears when Guam is in the Country field instead of the State field.
Products affected: SendPro® Enterprise

Issue

When shipping with PB Shipping API - USPS to Guam, the message "Error PB Shipping API: 1021003 Invalid/unsupported GU country Code" appears.

Cause

Guam is in the Country field.

Resolution

With PB Shipping API - USPS, Guam is considered a state/territory. In the Ship To address, put Guam in the State field and United States in the Country field.

UPDATED: November 18, 2021