Can't make your Joypad/USB/Generic pad or joystick work with the game? Try using the Steam controller settings.

Go this way:
Settings > Controller > General Controller Settings > Check the Generic Pad Configuration Support box > Then click on the detected controller box at the bottom, whatever it detected > Identify > Define Layout.

A config window will appear then set up the buttons to your liking, dont try to save the configuration by clicking on your gamepad's buttons, move your mouse away and the save options will appear at the bottom, click on it with your mouse and save then go try the game.

My USB adapter pad worked like this. Most likely it'll make some joysticks work too, or check the support box for Xbox and PS4 pads too, tho there's other ways to make them work too.

Also yeah, in case you're wondering this is here because it also counts as my review/feedback on the game, I'm gonna ask to please add more pad support for easy USB plug and play, many fighting games have it without these problems. Other than that awesome game.

EDIT: This is also helping with the Joystick problems
https://www.youtube.com/watch?v=3tSzaOje640