FreePBX dialplan documentation

is it possible to find documentation for the construction of dialplan freepbx?
Ideally interested flowchart dialplan, a brief description of macros and variables used.

You are looking for help with Asterisk Dialplan. Asterisk is the telephony engine that FreePBX runs on. Lots of help by searching with google and particularly this publication:

No, I want to read about dialplan freepbx
its entry points
about which macros are used and for what
about which variables are used

The source code of modules is your best bet. There is no documentation otherwise for this type of thing. Sorry wish we had time to do things like that.

it’s a pity
if freepbx was better documented - more developers and integrators have been able to use it with less effort

can you tell what I’m doing wrong?
I have 2 PBH communicated over IAX trunk

everything works fine, calls from one station to another act

but I need to process the call before it gets into the local content
I change the content for IAX-001 on the from-internal-iax001 (using the web interface)
I write to extensions_custom.conf
exten => s,1,goto(from-internal,${EXTEN},1)

then calls on trunks are not available
but the strange thing that the console CLI is empty - the station does not see the incoming call

where I go wrong?