Thank you for using this Woocommerce shipping plugin for USPS. This relies on the USPS Web Tools API, which is going to be phased out and eventually shut down. The new USPS API service does not include a Tracking API, unless you apply with a lengthy and manual vetting process for customers, so it is not a viable approach for this plugin to support.
Thank you for all the years that you have used this USPS plugin for your website. This plugin will be removed soon. There are alternative plugins available that use third party services to get USPS rates and tracking.