u/Accurate-Constant-53

So mario kart 7 works for download play with me and my friend, both our 3ds are modded and mk7 is a game cartridge. Mario kart 7 is the Only game that seems to work with download play and my friends 3ds cant seem to find any of my other games that i downloaded from the hshop when I create a room for download play, is it the difference being one is a game cartridge and one is from the hshop? help would be much appreciated