VoIP SIP trunk - incoming packet dropped "connection to be closed"
we have outgoing calls via SIP trunk working but incoming calls are dropped. In the packet monitor, the reason is "Packet dropped - connection to be closed". I run into this error on yet another location, another firewall, another provider, so I am curious what that could be. In the knowledgebase I haven't found neither helpful explanation of this error, nor troubleshooting steps.
SonicOS 18.104.22.168/22.214.171.124, NAT consistency Off, SIP transformations Off
Any advisory/idea would be highly appreciated.