What's the advantage of Pokémon calling for allies? Other than extra EXP, that is.

I had a problem with the game today. I tried to do a Wonder Trade and got the following error message: "In order to use online services, a newer version of the software is needed." It said to download a new version from the eShop, but I checked and there is no such new version. I also tried a System Update, and it said my system was up to date. What could the problem be?