Identify installation error
After activating Conversational Integration with Microsoft Teams users will get an option to install MS teams from messaging app integration page. During installation when the user clicks on install and if bellow error page is displayed with error code = 9, this is because the user on MS Team tenant does not have one of the required mentioned roles.
Please follow the doc to know more about Conversational Integration with Microsoft Teams plugin
Here is a link for store app plugin for Conversational Integration with Microsoft Teams plugin
Required Roles
Servicenow: virtual_agent_admin and external_app_install_admin or admin
Microsoft Teams administrator (one of the following): Global Administrator, Application Administrator, or Cloud Application Administrator
How to resolve the above error
Here is a Microsoft document that will help to add required roles to users. Once the user is assigned one of the above roles, they should be able to install/override MS Teams configuration.