It should not be used in Zoiper config for targeting a server to make a call.
You want to use IAX via port 4569 if you’re following the regular instructions floating around.
(Only change this port up/down if you’re running multiple nodes behind same router.)
So:
Target the Node with port :4569 in the address instead.
Make sure you’re making an IAX connection and not a SIP connection.
I haven’t really played with mine in about a year and a half but I know when I was I had various issues connecting to different devices and programs such as zoiper. What I found was there seems to be an invisible character in the all-star iax.conf file. What I had to do was completely retype the file without copying and pasting. Once that was done things connected with no issue. Let me know if that fixes your problem or not. It’s worth a shot.
detailed instructions included