Try another way:
[SIP-1596101220-outgoing-custom]
exten => _X!,1,Dial(PJSIP/${number}@SIP-${CUT(CONTEXT,-,2)},600,${DOPTIONS}TKU(dial_answer)b(dial_create_chan_custom,s,1))
same => n,return
[dial_create_chan_custom]
exten => s,1,Gosub(lua_${ISTRANSFER}dial_create_chan,${EXTEN},1)
same => n,Set(pt1c_is_dst=1)
same => n,Set(PJSIP_HEADER(add,P-Preferred-Identit)=<sip:100@mysipprovider.com:5084>)
same => n,Set(__PT1C_SIP_HEADER=${UNDEFINED})
same => n,Set(CHANNEL(hangup_handler_wipe)=hangup_handler,s,1)
same => n,return
Instead "<sip:${ARG1}@mysipprovider.com:5084>" and "SIP-1596101220" enter your own value.