First time that happened to us. Shipstation is only accepting Priority Mail and Express Mail which is more expensive than First Mail class. We have been using First Mail Class for a long time already. Is there something that we can do without having to pay more in shipping these orders?
Why do I keep getting errors in printing labels using First Mail Class?
Well you should be using Ground Advantage in place of First Class now. Check in your Settings > Shipping > Carriers and Fulfillment. Next to USPS, it will have a link displaying how many services there are enabled. Click that link to bring up the list of available services and make sure you have the box checked for USPS Ground Advantage and whatever else you want shown. Otherwise, something else must be going on.
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