Issue Summary

Open Microsoft Teams via web browser and add channel tab > Web site.
Add customer portal URL like https://<site name>.atlassian.net/servicedesk/customer/portal
The page shows "<site name>.atlassian.netで接続が拒否されました。" which means access denied by the site.
But the site does not have IP allowlist settings.
And this occurs even incognito mode, and any browsers.

However, the same can be accessed via MS Teams App.
 

Steps to Reproduce

1. Login to MS Teams via Web browser
2. Add channel tab > Website
3. Set the customer portal URL: https://<site name>.atlassian.net/servicedesk/customer/portal
4. The added tab shows that the Access is denied by the site

Expected Results

Customer portal is accessible by the MS Teams web.

Actual Results

Customer portal is not accessible by the MS Teams web.
It is accessible by the MS Teams App.

The below exception is thrown in the teams.microsoft.com.har HAR file:

Status Code:net::ERR_BLOCKED_BY_RESPONSE

And in the server, below message is logged when access is denied.

 message: Unable to infer the Help Center to use, as a help center reference is not set. In the future this will cause an exception.

Workaround

Open the channel tab via MS Teams App