Dotemu, Lizardcube, and Guard Crush Games working on a fix.
The Mr. X Nightmare DLC is currently available for Street of Rage 4, but a technical issue is preventing its purchase on the eShop.
Dotemu, Lizardcube, and Guard Crush Games are working on a solution:
We are aware of a technical issue affecting Nintendo Switch players from being able to purchase the [Streets of Rage 4] DLC. We are all hands on deck to remedy this issue for fans and will be posting updates on the ETA for when we anticipate the fix to be live.
Currently, our best projections are that the fix will come in following days but beyond that, we are unable to give a more accurate timeframe. This is extremely unfortunate for fans of the game who’ve waited patiently for the DLC and we apologize unreservedly.
For media outlets or content creators already in possession of a game code: please note that you will be able to play the game without this issue affecting gameplay.