Hello!
First, have you verified that you have the correct role for that subscription, that your trying to register an provider in?
Easy way to do this is browse the subscription in the portal, select "Access control (IAM)" in the left pane, select "Check access" and click on "View my access"
You will then se a list of all roles applicable to current account on this specific subscription :)
Verify that you have ATLEAST Contributor role on this subscription (owner works also).
Next you can select resource provider in the left pane of the same subscription to se if its already registered. If not you can also try selecting it here and click "Register".
Hope this is helpful Best Regards, Timmy Malmgren
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