When people visit my island it’s not working.

It could be you internet connection isn't great, that can lead to communication error. Or if the other person turns off their switch or their internet isn't working then that can happen too. Keep trying you'll get there!

Try visiting a dream address. If that works ur internet is OK if not then you need to sort out your own connection :)

Be sure to get as close to your Wi-Fi source (router) as possible. Use switch to check your connection speed. A or B NAT type typically required for hosting.

Also consider LAN connection (Google Nintendo Switch+LAN connection

Mine does that often too:(