question

I'm trying to send a payment request from my POS to our mini using a local connection (in the sandbox to a dev kit mini) but I keep getting a BadRequest response with no other information to help pinpoint the issue. I can successfully send Welcome Screen Requests and Order Display updates so I don't think it's a token issue. I've added the idempotency Key to the header, though I'm not sure what the parameters/restrictions other than it being 13 characters minimum. I'm using the endpoint /connect/v1/payments. Any ideas what it could be? Here's an example of the json request:

{
    "amount": 475,
    "capture": true,
    "deviceOptions": {
        "cardEntryMethods": [
            "MAG_STRIPE",
            "EMV",
            "NFC",
            "MANUAL"
        ],
        "cardNotPresent": false,
        "disableCashback": true,
        "disableRestartTransactionOnFail": true,
        "offlineOptions": {
            "allowOfflinePayment": true,
            "approveOfflinePaymentWithoutPrompt": true,
            "forceOfflinePayment": false
        }
    },
    "externalPaymentId": "C7EJMWx89TKF7pdtM3vuvYR42JpQWhMP",
    "externalReferenceId": "C7EJMWx89TKF7pdtM3vuvYR42JpQWhMP",
    "final": true
}