Just wanted to state this very clearly here since i’ve been getting a lot of confusion about it:
Unless you know what you are doing do NOT use the internal URL. Just use the normal URL. Internal URL is ONLY useful to you if you are unable to use the same hostname to access Home Assistant inside and outside of your network. If this situation applies to you, then set the Internal URL to the hostname used to access HA inside of your network and the other URL field to the URL you use to access HA outside of your network.