What does Bitpay's {"error": "Invalid token"} mean? I'm creating a web app that uses Bitpay for payments. I'm writing it in ruby (but that shouldn't matter), and have a class method bitpay_client with the body BitPay::Client.new('mYs3cretAPIkey'). 

Anytime I do BitcoinInvoice.bitpay_client.get("invoice/#{invoice_id}") I get the JSON {"error": "Invalid token"} back from the server. In Bitpay's documentation there's no mention of this message. I'm using the right api key, and I'm sure this is a real invoice. What does this message mean?
The error was my client connected to the wrong endpoint. This feature was undocumented at the time, but is now clearly documented. Kudos to Bitpay!