Getting 400 bad request: Authentication Message on Apple Business Chat

{
    "type": "interactive",
    "id": "f57d6be1-5329-43a4-b4e8-92babdda59o2",
    "v": 1,
    "sourceId": "urn:mbid:AQAAY4s8T/DWO0nUZxiqixyTXe3Q TRUNCATED",
    "destinationId": "6f7f7f2d-d4a6-46d5-TRUNCATED",
    "interactiveData": {
        "bid": "com.apple.messages.MSMessageExtensionBalloonPlugin:0000000000:com.apple.icloud.apps.messages.business.extension",
        "data": {
            "version": "1.0",
            "requestIdentifier": "7d8004b6-8827-4f32-b3f0-3a5fb36b203a",
            "authenticate": {
                "oauth2": {
                    "responseType": "code",
                    "scope": [
                        "email",
                        "profile"
                    ],
                    "state": "xyz",
                    "clientIdentifier": "abc",
                    "responseEncryptionKey": "MFYwEAYHKoZIzj0CJByFOYSigUnZ6nj",
                    "clientSecret": "client_secret"
                }
            },
            "images": [
            ]
        },
        "receivedMessage": {
            "title": "Sign In to Business Chat Sandbox"
        },
        "replyMessage": {
            "title": "Authentication Failed"
        }
    }
}

This is the sample payload I'm sending to the POST authenticate endpoint and I keep on getting 400 Bad Request. The payload seems correct as per the documentation. I'm also listing down the headers I'm using below:

Content-Type application/json
Destination-Id 6f7f7f2d-d4a6-46d5-TRUNCATED
Source-Id": urn:mbid:AQAAY4s8T/DWO0nUZxiqixyTXe3Q-TRUNCATED
id f57d6be1-5329-43a4-b4e8-92babdda59o2
version 1.0
Authorization Bearer eyazm...

The responseEncryptionKey is secp381r public key