[HeyAlex]

Hello,
When I open Joyn there is an error message in the upper right corner with URL Access Error. What is the problem?

[Klojum]

What is the problem?

The problem is that we here have no crystal ball to see what happens on your screen.
Start with providing Kodi's debug log (wiki) via a pastebin service, and we'll go from there.

[HeyAlex]

[font][font]Sry,
https://paste.kodi.tv/lihipahovo[/font][/font]

[Klojum]

I'm guessing that the Joyn add-on is coming from the kodinerds repository, which makes it a 3rd party add-on/repository.
In which case you will need to contact whoever created the Joyn add-on. I have no info here on who that might be.
Perhaps you can ask on the Kodinerds forum?