If Content Manager specifies a URL for the Web Client then the Teams integration will include this in the tab links when adding the integration to a channel. If the full web domain is not specified in the Teams integration manifest that was uploaded to install the integration then the process of adding a tab to a channel will fail.

In this example the domain intranet.acme.com must be included in the list of valid domains.

"validDomains": [
        "intranet.acme.com"
    ],