Does this issue persist all the time? Or what changes do before happened?
Do all callings with the first SBC have the same issue?
Above all, verify the connection between first SBC and direct routing.
- To validate the pairing using outgoing SIP options, use the SBC management interface and confirm that the SBC receives 200 OK responses to its outgoing OPTIONS messages.
- To validate the pairing using incoming SIP options, use the SBC management interface and see that the SBC sends a reply to the OPTIONS messages coming in from Direct Routing and that the response code it sends is 200 OK.
If the result is failure, please inspect the configuration of the first SBC.
Meanwhile, you could check the health dashboard for Direct Routing in Microsoft Teams admin center > Voice: Direct Routing. Then, analyzing the information by this article.
Besides, check UDP 3478-3481 ports and TCP 443 port are open in firewall.
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