How do I connect the Switch Pro Controller to the iPad?

I wanted to ask if that was possible and if so, how or why it hadn't worked for me so far or said that the controller could not be connected.

If not, does anyone know of good sites on which you could get used / remaining PS4 or Xbox controller? Would not like to spend 60 euro on it: /

Unfortunately I don't have an iPad, but I googled once. I found this, unfortunately I don't know if it is the right one and will help you further. But you can try it.