Event Hub Get Status with REST API - 401 Unauthorized

Question

I am attempting to use the REST API to get the Status of my event hub but it is returning "401 Claim is empty or token is invalid".

Using the C# example here: https://docs.microsoft.com/en-us/rest/api/eventhub/generate-sas-token#c I can build a SAS token for a POST

POST https://my-hubnamespace.servicebus.windows.net/my-eventHub/messages

And this works - 201 returned

Using the same SAS token I call:

GET https://my-hubnamespace.servicebus.windows.net/my-eventHub

401- Claim is empty or Token is invalid

What Claim is it referring to? I can't see any errors in my Portal.