Getting an error only when trying to run kivy GUI from remote terminal

Question

I'm testing some Kivy stuff to see how it works, and I want to edit and run the Kivy app remotely (using putty).

I'm on Raspbian GNU/Linux 10 (buster)

For simplicity's sake, here is the code I am using:

import kivy
from kivy.app import App
from kivy.uix.label import Label

class MyApp(App):
    def build(self):
        return Label(text="Test text.")

if __name__ == "__main__":
    MyApp().run()

When I run this locally, it works perfectly fine.

When I run it remotely with putty, I get the error * failed to add service - already in use?