Figured it out it not in the Xbox market posted an idea in the idea page of Xbox type mass effect 2 overlord dlc and you will find it and vote for it
I have had the same problem and reported it to Microsoft, I was told there have been several complaints with this error code when trying to buy the Overlord DLC for ME2.
The agent I am in contact with will keep me updated on this problem, so when he emails saying it has been resolved, then I will let you know.
My advice for now would be for yourself to report the problem to Microsoft.
I've been in contact with Xbox support and they have said they're looking into resolving this issue and will contact me with updates. If I hear anything I will post it here.
"And like you've said earlier, our specialist confirmed that you're not the only one who's getting this error. They found out that this is a known issue and the ticket for investigation has been raised to fully isolate the bottom of the issue by our engineers and developer to have this matter resolved. I certainly understand that you just want to get this DLC. and here's the best thing what I can do here for you while our developers and Engineers are taking care of this. I'll be leaving this case open and tag as my top priority so I can send you an update through email once this problem has been fixed."
June - last edited June
Confirmed issue for me as well.
I am in the NA region.
I have been able to re-license/purchase all Mass Effect 2 DLC on the Xbox Marketplace except for Overlord.
I have power cycled my Xbox One.
I have attempted to purchase Overlord on the Xbox One's Marketplace, within Mass Effect 2 (both in the Available Content and DLC menus), and on the Xbox Marketplace website itself from a PC browser. The purchase ability itself seems to be the issue; not sure if it's Xbox Live account-related, or something else.
EDIT: I spoke with Microsoft, and they are adamant we must speak with the game developers because the DLC purchase issues for backwards compatible games are most likely due to licensing or restrictions with the game developer. If that's the case, is there anything EA is doing to allow Overlord to be purchased once again? It seems crazy it's on the Marketplace and appears to be purchasable, it just isn't.
After a very lengthy, and otherwise fruitless conversation with Microsoft, they told me it "may" be because some backwards compatible add-ons cannot be purchased with the Xbox One (or on the Xbox Marketplace on either the One or on a PC). The only solution they gave me to try was to attempt to purchase it on the Xbox 360 itself and "hopefully" it will carry over to the Xbox One.
That solution won't work. I tried buying Overlord on my 360, in game and through the marketplace, neither would work. So whatever is going on has to do with the dlc.