Shippo has decided that it's a good rollout plan to have people who sign up for their service to get the newest version of their API, which is incompatible with the old version and not give them any way to downgrade. So if the software you want to use doesn't support this new API you are out of luck.

So we need to specify our API version in our header, so everybody gets the same version until we upgrade to the latest implementation.

All users who sign up for new Shippo accounts are running into issues using Shippo.