AADSTS90051: InvalidNationalCloudId

The national cloud identifier in the request isn't valid, for example a misspelled or mixed-up cloud name in your authentication library's settings.

How to fix it

Check the cloud or instance setting your library uses against the endpoint for your tenant's cloud.

Your tenant or subscription	Sign-in host
Commercial Microsoft 365 and Azure, and GCC tenants	`login.microsoftonline.com`
GCC High and DoD tenants, and Azure Government	`login.microsoftonline.us`

Note: Microsoft's row for this code doesn't mention clouds. The cause above is the common one in US government setups, so check it against yours.

“AADSTS90051 | InvalidNationalCloudId - The national cloud identifier contains an invalid cloud identifier.”

“Microsoft Entra ID for US Government | https://login.microsoftonline.us” (National clouds)

pip install fairfax
fairfax explain AADSTS90051 --tenant gcchigh      # or paste the whole error message

To find the commercial sign-in host in your code before it fails, run fairfax scan src/ --tenant gcchigh --azure government.