How to reslove The sign-in error code 53003

The sign-in error code 53003 means that Conditional Access policies set by the organization managing the resource (likely your organization) are blocking the external user from accessing the workspace. These policies can apply to external users if configured that way. A common misunderstanding is that Conditional Access policies only impact internal users, but they can also enforce requirements on external users accessing resources.

Here’s how to address this issue:

1- Review Conditional Access Policies:

Check your organization's Conditional Access policies in Azure Active Directory (or similar service) to identify if any restrictions are causing the issue. Common criteria include:

    Location: Access may be limited to certain IP ranges or geographic regions.

    Device compliance: Policies might require devices to be domain-joined or meet specific security                standards.

    Approved apps: Access could be restricted to specific browsers or applications.

2- Adjust Policies If Necessary:

If a policy is identified as the cause, consider:

    Adding an exception for the external user or their organization.

    Temporarily relaxing restrictions to allow access.

3- Coordinate with the External User’s IT Team:

If the issue is on their side, collaborate with the external user’s IT department to ensure their setup meets your Conditional Access requirements.

I recommend checking the Microsoft Entra Sign-in logs to determine which tenant’s Conditional Access policy is blocking access to the resources.