A user is unable to call any numbers, internal extensions or external numbers, when dialing from 3CX for Windows. When placing a call, it immediately fails with the message "Call failed" on the client. Restarting the client does not fix it. The workaround is to restart the entire device. Not sure what is causing this. Logs on the server say "Device Not Identified" [highlighted] but I'm not sure what this means.
10/22/2020 10:38:54 AM - [CM503027]: Call(C:10492): From: Extn:136 ("{{user}}" <sip:136@{{serverIP}}:0>) to T:Line:10000>>{{externalNumber}}@[Dev:sip:10000@{{providerURL}}:5060]
10/22/2020 10:38:54 AM - [CM503004]: Call(C:10492): Route 1: from L:10492.1[Extn:136] to T:Line:10000>>{{externalNumber}}@[Dev:sip:10000@{{providerURL}}:5060]
10/22/2020 10:38:54 AM - Call(C:10492): Call from Extn:136 to {{externalNumber}} matches outbound rule '10 Digit Prepend +1'
10/22/2020 10:38:54 AM - [Flow] Call(C:10492): has built target endpoint: Out#:>>Rule{10 Digit Prepend +1}>>{{externalNumber}} for call from L:10492.1[Extn:136]
10/22/2020 10:38:54 AM - [CM503010]: Call(C:10492): Making route(s) from Extn:136 to <sip:{{externalNumber}}@{{serverIP}}:0/UDP>
10/22/2020 10:38:54 AM - [CM505001]: Endpoint Extn:136: Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [3CXPhone for Windows 16.3.0.179] PBX contact: [sip:136@{{serverIP}}:5060]