In addition to the guidance issued by CBP, they also issued FAQs on the new postal code requirement for shipments from China (see below). These requirements are effective on March 18, 2023.
CSMS # 55423161 – UFLPA Region Alert and Postal Code Requirements FAQs
U.S. Customs and Border Protection has published a Frequently Asked Questions document related to the upcoming UFLPA Region Alert and Postal Code Requirements that will go into effect on March 18, 2023.
The new FAQ document can be found at https://cbp.gov/document/faqs/uflpa-region-alert-faqs