This operation withdraws an activation before it has been submitted to Tower/ACE, physically deleting its record. It succeeds only when the activation is in one of these statuses: ACCEPTED, PENDING_VALIDATION, FAILED_VALIDATION, or STAGED. Unlike POST /cancel, this operation always releases the environment-version and hostname-set-version locks held by the activation (unless another activation already holds them), and it permanently removes the activation record rather than marking it ABORTED — a subsequent GET for the same activation ID returns a 404. Activations that have progressed beyond these statuses must use POST /cancel instead; calling DELETE on them returns a 409 error. Targeting an already-ABORTED activation also returns a 409 error.