Problem between two servers

Hi guys, It’s my first time here. I have this problem for a long time, I went to the FreePBX forum, but with time I discovered that the problem is deeper. I saw some peoples that have the same problem that I have, but their topics didn’t help me at all.
So now I’m here.
So my problem is:
I have two Asterisk servers that have to transfer calls between them. It works well but sometimes it just stops working, so looking in the logs I saw that happens when the server changes the IP. So we restart the server and it comes back to life. But now I have another problem, sometimes I can transfer calls between them, it plays a message like ‘all circuits are busy now, please call later’.
Looking the logs I saw that line:
[2021-03-23 11:04:06] WARNING[15775][C-00000433] app_dial.c: Unable to create channel of type 'IAX2' (cause 20 - Subscriber absent)
I searched about it and saw that it about register the trunk, but I have no idea how I made this because, in some sites, they say to make it in ‘sip.conf’ but the file has the instruction to not make any modification on it. And I don’t know how to can I do this in the FreePBX.
If I restart the asterisk it works again, but I don’t want to restart the server every time that it occurs.
Thank you guys, I hope that you can help me.
Ps. I am pretty new in the FreePBX and Asterisk world. So sorry if I look like a newbie, its because I am :slight_smile:

You’ve said you are using IAX, so why are you modifying sip.conf?

The “do not modify” question relates to a restriction imposed by FreePBX, so you need to take that back to the FreePBX forum.

IAX is little used, probably hasn’t been maintained for years, and probably never had any support for people who try to operate servers on consumer grade internet accounts.

Your easiest solution is probably to set up a VPN, so that Asterisk sees a stable address structure.

Typically FreePBX includes a custom configuration file from the main file. Look for #include directives. You can continue section <section> using:

[<section>](+)

It does appear that IAX has support for consumer grade internet connections:

If you look a bit up from there, you will also see where you configure registrations for IAX, but note that one side will still need an address can be accessed through a domain name, or is static.