Adding a SmartApp fails in the Android app - check your network connection error

I have registered a test SmartApp through the SmartThings developer portal and deployed to test successfully.

This is an example app from the SDK documentation: https://github.com/SmartThingsCommunity/smartapp-example-every-setting-nodejs

My server is up and running, I have a public URL through ngrok (configured in the SmartApp registration, etc…)

When I add the SmartApp through my Android device (which is showing up correctly after enabling Developer Mode) - I get a message for “Processing”, then an error for “Sorry we are having trouble connecting. Check your network connection”

I can add other SmartApps without any issue.

I see traffic to the example SmartApp service through the local log files, example:

2020-12-30T20:13:09.717Z debug: CONFIGURATION/INITIALIZE REQUEST: {
  "lifecycle": "CONFIGURATION",
  "executionId": "7cc2cdae-ff33-2f0a-3c8d-a27fbb904872",
  "appId": "94fd8427-c2e2-4aae-a3a6-913108c210d6",
  "locale": "en",
  "version": "0.1.0",
  "client": {
    "os": "android",
    "version": "1.7.57.23",
    "language": "en-US",
    "displayMode": "LIGHT",
    "timeZoneOffset": "",
    "supportedTemplates": [],
    "samsungAccountId": ""
  },
  "configurationData": {
    "installedAppId": "5fd387a9-5737-4483-8b46-0bf642ecce48",
    "phase": "INITIALIZE",
    "pageId": "",
    "previousPageId": "",
    "config": {},
    "isResubmit": true
  },
  "settings": {}
}
2020-12-30T20:13:09.739Z debug: RESPONSE: {
  "statusCode": 200,
  "configurationData": {
    "initialize": {
      "id": "52ef54d8-f991-4ef8-9bf0-733e32143fc6",
      "firstPageId": "indexPage",
      "permissions": [
        "r:devices:*",
        "r:locations:*",
        "r:scenes:*"
      ],
      "disableCustomDisplayName": true,
      "disableRemoveApp": false
    }
  }
}

So looks like requests are being routed and hit my service. However I dont see any log entries in the SmartThings developer portal ‘Live Logging’.

Any ideas to further troubleshoot?