Target SD Card: one of the Memory Cards Compatible With 3DS, such as a 32GB SD Card. For New 3DS, check MicroSD Cards Compatible With New Nintendo 3DS.

Nintendo officially only supports memory cards up to 32GB -- no matter whether you're using SD or microSD cards and which 3DS iteration you own.

To fix Memory Error 13-71 in Modern Warfare and WarZone on Xbox or PC, delete the Regiment tag, remove yourself from active regiments, disable crossplay, etc.