Getting error when exporting Azure sql database using az cli?

I am getting an error when i try to export an Azure sql database . I am using the folowing to export :

    az sql db export -s pds1 -n pdb1 -g resourcegroup --admin-password "password" --admin-user "username" --auth-type ADPassword --storage-key accesskey --storage-key-type StorageAccessKey --storage-uri "storage accname.blob.core.windows.net/folder1/myBacpac.bacpac"

The error is :

Message: The ImportExport operation failed due to 'An error occurred while communicating with the SQL Server using AdPassword-login: Could not discover a user realm.',

Any ideas on this ?