how to avoid 603 decline

[lcomao]

when i make call to web, sometimes web can not accept and return 603 decline, log like below:

layouts__BasicLayout.df33f3ae.async.js:1 >>>sip stack events listener Event: i_new_call
sip.min.js:1 State machine: s0000_Ringing_2_Terminated_X_Reject
sip.min.js:1 === INVITE Dialog terminated ===
sip.min.js:1 PeerConnection::stop()
sip.min.js:1 State machine: tsip_transac_ist_Proceeding_2_Completed_X_300_to_699
sip.min.js:1 SEND: SIP/2.0 603 Decline
Via: SIP/2.0/WSS 47.99.185.209:47060;rport=47060;branch=z9hG4bK2UgX82Ncv2rpQ
From: "17316375517"sip:[email protected];tag=190jKa55ZvyNg
To: sip:[email protected];rtcweb-breaker=no;transport=wss;tag=BnbuPTBGVQ2y6TgQyEsL
Call-ID: 6378b4c1-8bd8-123a-45a4-00163f004e49
CSeq: 41030319 INVITE
Content-Length: 0
Reason: SIP; cause=603; text="Decline"