You can troubleshoot JavaScript in Teams using the web based version of teams via: https://teams.microsoft.com
If you're building a configuration tab and get the following message:
We couldn't save your tab settings.
You can bring up F12 Developer Tools to see what's going on and even debug your JavaScript eg:
Clicking on the configuration.htm you can see I've forgotten to use the SSL ngrok endpoints - which was the cause of this error. This is a prerequisite referenced here: https://docs.microsoft.com/en-us/microsoftteams/platform/concepts/tabs/tabs-configuration
