Setting APN doesn't work because of a typo ($c vs. $x). Could you please
provide a package I can test before you notify upstream? I have to say
I'm very surprised noone bothered to report it yet, comgt's scripting
language is so much better than chat's, doesn't anyone use this feature?

Log:
joco@wicklow:~$ COMGTAPN=internet comgt -d /dev/ttyUSB1 -v APN
...
comgt 20:11:11 -> @0109 let $x=$env("COMGTAPN")
...
comgt 20:11:11 -> @0218 send "AT+CGDCONT=1,\"IP\",\"
comgt 20:11:13 -> @0279 waitfor 20 "OK","ERR"
...
comgt 20:11:13 -> @0394 print "ERROR entering APN
ERROR entering APN
comgt 20:11:13 -> @0426 print "The COMGTAPN env variable is not set
The COMGTAPN env variable is not set
comgt 20:11:13 -> @0476 exit 1

I fixed the variable name ($c=>$x) and also noticed that a double
quotation mark is missing and it was sending "send $x" literally to the
modem. So the correct APN setting is:

send "AT+CGDCONT=1,\"IP\",\""
send $x
send "\"^m"