Error transferring calls with VOIP.MS SIP trunk invalid_destination, no CDR logged at VOIP.MS

Support Help
1

Hi I have my account setup with custom telephony. It’s connected to a SIP trunk at VOIP.MS. Incoming calls work fine, but when I try to transfer a call it fails right away. No outgoing CDR is logged at VOIP.MS, only the incoming call to retell is logged. This is the exact error in Retell: error: Error transferring call, SIP status code: 486 SIP error category: user_busy Error: twirp error unknown: INVITE failed: sip status: 486: Busy Here

Appreciate any help. The transfer number is in E.164 format, and VOIP.MS is set to accept that format. Thanks.

2

Hey @blake

A SIP 486 (user_busy) error with no outbound CDR at VOIP.ms strongly suggests the call isn’t even reaching VOIP.ms termination — it’s being rejected at the SIP trunk level.

Check your termination setting in your SIP trunking provider, and make sure you provide the right termination url to Retell.

VOIP.ms often requires authorized IPs. Whitelist Retell’s IP block: 18.98.16.120/30, 143.223.88.0/21, 161.115.160.0/19.

if using cold transfer, VOIP.ms must be configured to allow SIP REFER and PSTN transfer with the transferee’s number as caller ID.

Since no CDR is logged at VOIP.ms, the trunk is rejecting before accepting.