I am making a rest call in powershell that retrieves emails as follows:

            az rest --method GET --uri "https://graph.microsoft.com/v1.0/users/<email_object_id>/mailFolders/<folder_id>/messages" --headers "Authorization: Bearer  <access_token>"

The access token is retrieved from graph explorer.
I get the error

   Failed to parse string as JSON
   ERROR: not enough values to unpack (expected 2, got 1)

Could it be the access token ?

What would cause this and how can i fix it ?