To clarify how a Data Holder should respond in the instance when no x-min-v header is submitted. For example; a Data Holder supports versions 1 and 2 of their endpoint and a Data Recipient sends a request with x-v = 3.
Should the Data Holder respond with a 406 error message or with the maximum version they support? In this scenario v2.
x-min-v header is supplied it means that the client only supports a single version specified in
x-v so if the holder cannot supply that version then they should respond with a 406.
In the scenario you outline in your question you would supply a 406.