MPCX MPK88 setup

I am a beginner producer(literally starting from square one. I was wondering if anyone could answer a question about the MPCX for me, I’m having a bit of trouble with my set up.
I am attempting to use my Akai MPK88 to create a melody for my beats while attached to my MPCX in standalone mode and I can’t get it to work in Midi mode. Only in keygroup mode does it work.(as I am able to assign a keygroup program) However, I can’t edit what I play in grid mode as I should be able to as in with playing drums on the pads. When I attempt to play any keys in midi mode bothing comes out at all. I also cant assign an instrument to it in midi mode either. Its pretty confusing.
I’ve looked in all of the manuals and the MPC Bible as well and can not find an answer to this issue. Can you guys help me out?

Midi mode is to send midi data to external gear, synth, sound module, etc. so with no external gear connected to the midi out port on the back of your MPC, there will be no sound. I have a MPK25 and it works fine for drum kits, key groups, and expansions. I use midi mode when I want to use my iPad as a sound module, and the MPK25 works fine.