Here's a video to help learn about half-pedal.

https://www.youtube.com/watch?v=XUOUSfClpWs

What's going on is that sustain will get values between 0 and 127 (and all between) instead of an "on and off" type sustain which gives you either just 0 or just 127.

Here's a thread covering your Yamaha sustain options:

https://www.yamahasynth.com/forum/fc3a-vs-fc4a-best-for-montage

It is best to stick with the OEM brand pedal - the premium is not high in this category. If using a simple "on off" switch - you need to be sure the polarity matches what Yamaha expects or has a switch to toggle the polarity to support "all" keyboards. The sustain pedal will generally list compatibility by manufacturer (Yamaha, Roland, etc).

The M-Audio SP-2 is an example of an "on/off" type switch that has a toggle switch on the bottom to set the polarity. It does not support "half-pedal". I would shy away from 3rd party pedals if half-pedal is what you're after since the resistance range has to match which is not as universal as an on/off switch with only one consideration (polarity meaning normally off or normally on when your foot is not pressing the pedal).

Geoffrey,
Welcome to Yamaha Synth.
Remember, It’s your music. The recommended pedals are shown in the Owner’s Manual on Pages 11-12.

Thanks Jason and Bad Mister.

You guys are truly blessings to others!

Thanks!!!