Can only call one way

Hello all.
I am trying to connect an asterisk and freepbx server together via iax2 trunk. I can call from the asterisk to the freepbx, however when trying to go from the freepbx to the asterisk, the call says the line is busy, the trunks all show as up, and the asterisk with debug on picks up the call, tcpdump shows data too.

when running a debug i get the following

VERSION         : 2
CALLED NUMBER   : 538
CODEC_PREFS     : (ulaw|alaw|gsm)
CALLING NUMBER  : 6000
CALLING PRESNTN : 0
CALLING TYPEOFN : 0
CALLING TRANSIT : 0
CALLING NAME    : 6000
LANGUAGE        : en
USERNAME        : pbxout
FORMAT          : 4
FORMAT2         : ulaw
CAPABILITY      : 14
CAPABILITY2     : Unknown
ADSICPE         : 2
DATE TIME       : 2022-01-05  13:30:46
CAUSE           : No such context/extension
CAUSE CODE      : 3

whats odd is my extensions.conf has a line for:
exten => 538,1,dial(SIP/538)
and my sip.conf
[538]

type=friend

username=538

callerid=538

secret=538

context=internal

host=dynamic

allow=all

any ideas?
thanks

Why have you provided sip.conf when it is an IAX call that is failing?

the iax.conf contains the trunk for the two servers, the sip.conf contains the sip accounts for the asterisk box that im dialing from the freepbx, i have just gotten it working by adding a context line to the config file, now the calls connect through however no voice and the line drops.