On February 23, 2018, USPS will remove APIs that support the creation of shipping labels without postage. In anticipation of this change, we’re removing this functionality from the Magento Admin in our next release, and consequently, merchants will not be able to natively create and print USPS shipping labels that do not have postage applied. We anticipate that the next release will go out within the next 2-3 weeks.
More information is available from USPS at: https://www.usps.com/business/web-tools-apis/letter-to-customers-usps-web-tools-label-api-eliminatio...
