a tip for newcomers: if yer 3DS/2ds has an unable to update error it's QUITE POSSIBLY BC your wifi's too advanced for it. HOWEVER you can use your phone as a hotspot, it doesn't burn thru any data. this saves you from going on a wild goose chase in search of supported nets...
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also i'm aware a slightly complicated process can alter your wifi to support it...
Hmm. don't know if I ever had this problem.