Someone already asked this questions about Magento 188.8.131.52, and can be found at the following link Magento 184.108.40.206 USPS API First Class No Longer Working
I tried following the steps found on that question and the steps linked to from that post at the blog.shipperhq.com site and couldn't get the first class option working again.
The steps found at the blog.shipperhq.com mentioned for Magento 2.0.X you should edit the following file, vendor/magento/module-usps/Model/Usps.php but I'm running Magento 2.1.5 and don't have that file.
Does anyone have the proper steps for a workaround that work with Magento 2.1.X? For more context about the issue, please click the link at the top of my question.