Do you have the Yamaha Steinberg USB Driver installed? Because it's possible to record audio even without it although only one channel will be presented and not all of the USB channels for individual Parts. Please verify you have installed the Yamaha Steinberg USB Driver.

Also, I'm not sure what firmware you have installed on the MODX. This shouldn't create any issue but it's always best to use the latest available firmware in the MODX downloads section (on yamaha.com for your region).

Since FL Studio is available for both Mac and Windows - it may help to elaborate what host computer you are using since this may slightly influence the specifics.

I have just solved my issue! Thanks for providing the most extreme surface level answer. Of course I had the drivers installed and everything, I have done monumental research to figure this problem out. Your answer is basically like when a very complex computer problem happens and someone says "did you try turning it off and on..." OF COURSE I DID 1000 TIMES! Anyways, What solved it finally was in FL Studio in the output section it shows 3 different modx outputs. I had previously only been selecting one of them to send info to port 1. I changed all of them to port 1 and now it works!

This post online made it click for me... for anyone having this problem:

T"he MODX USB connector can transmit/receive MIDI and audio. It acts like a USB audio interface so If you want to use it to transfer audio into FL Studio then you need to set it as your audio interface within FL Studio. If you’ve already got a decent audio interface then it’s probably best to use that and connect the 1/4” audio outs from the MODX into the interface and use the MODX USB interface for MIDI only.

Then open the midi out plugin in FL Studio that sends MIDI to the MODX via port 1. Make sure it also receives audio inputs from the inputs on your audio interface the MODX is plugged into.

If that doesnt make sense for someone heres step by step what I did.

With the yamaha drivers installed, you get 3 outputs that show up in FL studio. I had been previously only setting the bottom one (MODX-3) to port 1. What solved this problem was selecting the top one (MODX-1) in the output section and routing that one to Port-1. I then changed my audio device to Yamaha steinberg USB audio, and plugged my headphones into the keyboard. I then opened the Midi out plugin in FL Studio and selected port one. Viola, I now can click in midi notes and it uses the sounds from the MODX!

Glad you got it solved.

MODX has 3 ports.

MODX-1 is the internal tone generator. The port you want to send MIDI notes to play sounds using the internal keyboard (tone generator sounds).

MODX-2 is for DAW Remote control

MODX-3 is for accessing devices connected to the 5-pin DIN MIDI IN/OUT connectors while in USB mode. It's simply a pass-through to these connectors so your DAW/computer can communicate with any devices you have connected through those ports.

... I didn't find anything insulting from James. Just normal venting that comes out of frustration which I can empathize with. Some people work differently under this kind of pressure than others.

I do commend James for sticking with it and then doing his best to fill in the forum what was done to correct the problem. Seems like a lot of good stuff is happening as well. I'll choose to focus on the good stuff.