If you are looking for the actual of the major Dragon Age 2 DLCs rather than technical fixes, here is what they cover:
EA transitioned accounts from the old BioWare Social Network to the EA App, breaking old verification links.
Community members have developed several "manual" methods to bypass these authorization checks: DA2 DLC Unauthorized - How do I activate it? - EA Forums
While these tools were born out of a desire for software preservation, they highlighted a massive flaw in early 2010s DRM: when the verification servers die, the consumer's purchase often dies with them. The Modern Solution: EA Retires Legacy DRM