It seems like you've taken some steps to enable cross-tenant collaboration but are encountering issues with accessing a OneNote page within an External (other company) channel. Here are some additional steps you can consider:
- Verify OneNote Permissions: Ensure that the external users have the necessary permissions on the OneNote page. Double-check the sharing settings and confirm that the external users have at least view or edit permissions.
- Check External Sharing Settings: Review external sharing settings not only within your collaboration platform but also within OneNote. Confirm that external sharing is allowed on the specific notebook or page.
- Consistent Authentication: Confirm that both companies use consistent authentication methods. If one company is using multi-factor authentication or other additional security measures, it might affect the authentication process.
- Cross-Tenant Permissions: Check and ensure that the cross-tenant permissions are set up correctly not only in your collaboration platform but also in Azure AD or any identity provider you're using.
- Browser Compatibility: Confirm that the users are using supported browsers, and suggest trying different browsers to rule out browser-related issues.
- App Version Consistency: Ensure that all users have the latest version of the collaboration app. Inconsistent app versions could lead to compatibility issues.
- Logging and Monitoring: Implement logging and monitoring to capture detailed information about the authentication process. This could provide insights into any specific errors or issues occurring during authentication.
- Support Channels: If the issue persists, reach out to the support channels of your collaboration platform and OneNote service. They might have specific troubleshooting steps or insights into common issues related to cross-tenant collaboration.
By systematically addressing these points, you can narrow down the potential causes of the authentication issue and work towards a resolution.