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• https://forums.elderscrollsonline.com/en/discussion/683901
I believe the DLC officially launches on the 1st of November but you collected it from buying the Heroes of High Isle Reward Bundle, though because this concerns a purchase and I am unfamiliar with that error code I would wait for @ZOS_Kevin to reply
You probably didn't notice it, but the DLC went to the Collections after you claimed the reward bundle. Once the DLC launches, you will get immediate access to the content.
As the OP has gotten their question answered regarding getting the Firesong DLC, we will go ahead and close this thread. For further information please see our FAQ linked below.