Can not delete Test Plan / Suite in Azure Dev Ops

Question

Can anyone help me to delete items below?
I already set the permissions, may I missing something?

Error message
Failed to delete work item: 8423. Error Details: You don't have sufficient permissions to delete this work item. You must have work item and test artifacts delete permissions.

Answer 1

As mentioned by Daniel Mann, Test Plans subscription is required to manage Test Plans.

Documentation