Can not make a call

Hi guys!
could you please help me with this.I setup a2billing in trixbox successfully and when I dial the number.It reads the account cash, and asks me for the number.
then, after I dial the number, it says :
-----Playing ‘prepaid-dest-unreachable’ (language ‘en’)

it show full log:

[Dec 7 20:28:07] VERBOSE[5161] logger.c: – Launched AGI Script /var/lib/asterisk/agi-bin/a2billing.php
[Dec 7 20:28:08] VERBOSE[5161] logger.c: – Playing ‘prepaid-you-have’ (escape_digits=#) (sample_offset 0)
[Dec 7 20:28:09] VERBOSE[5161] logger.c: – <SIP/3556993614-00000023> Playing ‘digits/1.gsm’ (language ‘en’)
[Dec 7 20:28:09] VERBOSE[5161] logger.c: – <SIP/3556993614-00000023> Playing ‘digits/hundred.gsm’ (language ‘en’)
[Dec 7 20:28:10] VERBOSE[5161] logger.c: – Playing ‘dollars’ (escape_digits=#) (sample_offset 0)
[Dec 7 20:28:11] VERBOSE[5161] logger.c: – <SIP/3556993614-00000023> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
[Dec 7 20:28:34] VERBOSE[5161] logger.c: – Playing ‘prepaid-dest-unreachable’ (escape_digits=#) (sample_offset 0)
[Dec 7 20:28:37] VERBOSE[5161] logger.c: – <SIP/3556993614-00000023> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
[Dec 7 20:28:47] VERBOSE[5161] logger.c: – <SIP/3556993614-00000023> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
[Dec 7 20:28:57] NOTICE[5161] res_agi.c: FONALITY: Hangup detected, AGI terminates.
[Dec 7 20:28:57] VERBOSE[5161] logger.c: == Spawn extension (a2billing, 441, 3) exited non-zero on ‘SIP/3556993614-00000023’

trixbox1*CLI> sip show users
Username Secret Accountcode Def.Context ACL NAT
outbound1 06081989 default No RFC3581
4901472037 4180668786 4901472037 a2billing No Always
3556993614 2807649060 3556993614 a2billing No

== Using SIP RTP CoS mark 5
– Executing [[email protected]:1] Answer(“SIP/3556993614-00000024”, “”) in new stack
– Executing [[email protected]:2] Wait(“SIP/3556993614-00000024”, “2”) in new stack
– Executing [[email protected]:3] DeadAGI(“SIP/3556993614-00000024”, “a2billing.php”) in new stack
– Launched AGI Script /var/lib/asterisk/agi-bin/a2billing.php
– Playing ‘prepaid-you-have’ (escape_digits=#) (sample_offset 0)
– <SIP/3556993614-00000024> Playing ‘digits/1.gsm’ (language ‘en’)
– <SIP/3556993614-00000024> Playing ‘digits/hundred.gsm’ (language ‘en’)
– Playing ‘dollars’ (escape_digits=#) (sample_offset 0)
– <SIP/3556993614-00000024> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
– <SIP/3556993614-00000024> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
– Playing ‘prepaid-dest-unreachable’ (escape_digits=#) (sample_offset 0)
– <SIP/3556993614-00000024> Playing ‘prepaid-enter-dest.gsm’ (language ‘en’)
== Spawn extension (a2billing, 4901472037, 3) exited non-zero on ‘SIP/3556993614-00000024’

I dont know how things work, please give me a tip on this.
thank you !