API request - Hippa error message

We've been making api requests over the last several months without problem to 'api.knack.com.'

As of yesterday afternoon, we've started getting the following error message (with a 400 Bad Request status):
HIPAA accounts and applications may only be accessed through usgc-api.knack.com

I have tried making an api call to 'usgc-api.knack.com', but get a 500 status code back with no helpful information. I can't find anything about this requirement in the documentation (unless you're using oauth.)

Anyone know anything about this or how to fix it?