MS teams calling bot fails with internal server error

Hi there, 

I'm attempting to get a calling bot running locally by following this repo/guide: https://github.com/vasalis/TeamsRecordingBotAndAzureCongitiveServicesAtWork/tree/master/00_RecordingBot

I've got the bot running locally but when I send a Postman request, I get the following error:

ScenarioId: {
  "oldResource": {
    "@odata.type": "#microsoft.graph.call",
    "state": "establishing",
    "direction": "outgoing",
    "callbackUri": "https://teamspoc.eu.ngrok.io/0/api/calling/notification",
    "callRoutes": [],
    "source": {
      "@odata.type": "#microsoft.graph.participantInfo",
      "identity": {
        "@odata.type": "#microsoft.graph.identitySet",
        "application": {
          "@odata.type": "#microsoft.graph.identity",
          "displayName": "RecordingBot.Services",
          "id": "e9a3211c-7fe5-499c-ac09-daf37aa858fc"
        },
        "acsUser": null,
        "spoolUser": null,
        "phone": null,
        "guest": null,
        "encrypted": null,
        "onPremises": null,
        "acsApplicationInstance": null,
        "spoolApplicationInstance": null,
        "applicationInstance": null
      },
      "participantId": null
    },
    "targets": [],
    "requestedModalities": [
      "audio",
      "video"
    ],
    "mediaConfig": {
      "@odata.type": "#microsoft.graph.appHostedMediaConfig",
      "blob": "{\"mpUri\":\"net.tcp://teamspoc.eu.ngrok.io:23991/MediaProcessor\",\"audioRenderContexts\":[\"b72e0949-7228-489f-bb49-966b26deb2a1\"],\"videoRender
Contexts\":[null],\"audioSourceContexts\":[null],\"videoSourceContexts\":[],\"dataRenderContexts\":null,\"dataSourceContexts\":null,\"supportedAudioFormat\":\"Pcm
16K\",\"videoSinkEncodingFormats\":[\"Yuv\"],\"mpMediaSessionId\":\"1ae2157d-f1fe-4c60-983f-f4fb562e5309\",\"regionAffinity\":null,\"skypeMediaBotsVersion\":\"1.1
9.0.0025\",\"mediaStackVersion\":\"2020.18.1.16\",\"mpVersion\":\"7.2.0.9053\",\"callId\":\"44d35298-87e3-400f-a401-90e8715b23d4\",\"receiveUnmixedMeetingAudio\":
true}"
    },
    "chatInfo": {
      "@odata.type": "#microsoft.graph.chatInfo",
      "threadId": "19:meeting_M2JmYjRhYzMtZDZlZi00M2UyLTk4YzEtMzlhOGY4OWE3MjY1@thread.v2",
      "messageId": "0"
    },
    "callOptions": {
      "@odata.type": "#microsoft.graph.outgoingCallOptions",
      "isContentSharingNotificationEnabled": null,
      "isWatermarkSupported": null,
      "hideBotAfterEscalation": null,
      "allowGuestToBypassLobby": null
    },
    "meetingInfo": {
      "@odata.type": "#microsoft.graph.organizerMeetingInfo",
      "organizer": {
        "@odata.type": "#microsoft.graph.identitySet",
        "user": {
          "@odata.type": "#microsoft.graph.identity",
          "id": "f353f265-2c71-41c1-9537-9df59b7f2965",
          "tenantId": "<omitted>"
        }
      }
    },
    "tenantId": "<omitted>",
    "myParticipantId": "2fd4cc44-e7cf-4acd-8b1a-42d05515d207",
    "callChainId": "e6c9c043-85e6-4d4f-ad16-b522e9f18156",
    "id": "671f6100-cd61-4ab4-9fff-4ce505a65789"
  },
  "newResource": {
    "@odata.type": "#microsoft.graph.call",
    "state": "terminated",
    "resultInfo": {
      "@odata.type": "#microsoft.graph.resultInfo",
      "code": 500,
      "subcode": 3003,
      "message": "Server Internal Error. DiagCode: 500#3003.@"
    },
    "chatInfo": {
      "@odata.type": "#microsoft.graph.chatInfo",
      "threadId": "19:meeting_M2JmYjRhYzMtZDZlZi00M2UyLTk4YzEtMzlhOGY4OWE3MjY1@thread.v2",
      "messageId": "0"
    },
    "meetingInfo": {
      "@odata.type": "#microsoft.graph.organizerMeetingInfo",
      "organizer": {
        "@odata.type": "#microsoft.graph.identitySet",
        "user": {
          "@odata.type": "#microsoft.graph.identity",
          "id": "f353f265-2c71-41c1-9537-9df59b7f2965",
          "tenantId": "<omitted>"
        }
      }
    },
    "tenantId": "<omitted>",
    "callChainId": "e6c9c043-85e6-4d4f-ad16-b522e9f18156",
    "id": "671f6100-cd61-4ab4-9fff-4ce505a65789"
  },
  "resourcePath": "communications/calls/671f6100-cd61-4ab4-9fff-4ce505a65789",
  "additionalData": {
    "scenario-Id": "4a1d92d3-b494-4b32-b35c-deec227fa47c",
    "x-Forwarded-For": "51.140.70.139",
    "x-Forwarded-Host": "teamspoc.eu.ngrok.io",
    "x-Forwarded-Proto": "https",
    "x-Microsoft-Skype-Chain-Id": "e6c9c043-85e6-4d4f-ad16-b522e9f18156",
    "x-Microsoft-Skype-Message-Id": "ab717a35-7f75-4876-b3b6-f0c60e6e66dc",
    "accept": "application/json",
    "accept-Encoding": "gzip",
    "authorization": "Bearer <omitted>",
    "host": "localhost:9441",
    "user-Agent": "Microsoft-Skype/3.0,(Calling/1.0)",
    "content-Length": "973",
    "content-Type": "application/json",
    "callbackUri": "https://localhost:9441/0/api/calling/notification"
  }
}

Does anyone know where this might be failing?

Thanks.