[Serusers] SER -> Asterisk ==> Call failed: 403 Forbidden

Hi all, I have a problem with forwarding calls from SER to Asterisk. XXX -> SER -> Asterisk -> YYY I have XXX UAC which is registered in SER and YYY UAC which is registered in Asterisk. When I forward call from SER to Asterisk I get "Call failed: 403 Forbidden" from Asterisk. Everything works fine if I register XXX UAC in Asterisk too (SER forwards call to Asterisk and it works). I think I don't understand this registering SER to Asterisk and other way and I would appreciate if someone could help with this. Best regards sip.conf [general] port=5060 ; Port to bind to bindaddr=0.0.0.0 ; Address to bind SIP channel to context=ser autocreatepeer=yes register => 2000:1234@ser_ip_address/5678 [ser_ip_address] type=friend username=2000 secret=1234 fromdomain=srce.hr host= ser_ip_address [5678] type=friend username=5678 host=dynamic canreinvite=no extensions.conf [ser] exten => 5678,1,Dial(SIP/5678,20) exten => 5678,2,Voicemail2(u5678) exten => 5678,3,MusicOnHold() exten => 5678,102,Voicemail2(b5678) exten => 5678,103,Hangup