We are troubleshooting intermittent missed incoming calls to a 3CX iOS user.
System:
- 3CX V20.0.1277 SP10
- Self-hosted
- 4SC / Free
- iOS app: 3CXPhone for iOS 20.0.22.153
- iPhone running iOS 26.6.1
- Extension 1002
- Incoming calls route through Ring Group 8001
- Ring Group ring time: 20 seconds
- No answer routes to voicemail
The problem is intermittent. Some calls ring the 3CX iOS app normally and can be answered, while other calls do not produce any visible or audible incoming-call alert on the iPhone and eventually route to voicemail.
We enabled Verbose logging on both the PBX and iOS app and reproduced the issue.
PBX evidence from an earlier failed controlled test:
- The PBX routed the call to extension 1002.
- The Mobile Client path returned SIP 180 Ringing.
- The Dialer path also returned SIP 180 Ringing.
- The extension route remained active for approximately 20 seconds and terminated due to timeout/no answer.
- The call then routed to voicemail.
We also captured a successful call for comparison. The initial PBX routing and 180 Ringing behavior was substantially the same, but on the successful call the actual iOS client subsequently connected as "3CXPhone for iOS 20.0.22.153".
We then reproduced another failure at approximately 19:55 EDT with iOS Verbose logging enabled.
For that failed call, the iOS Incident Report shows:
19:55:01.276 - Received push
19:55:01.278 - CallKit attempting to present incoming call
19:55:01.361 - CallKit presented the incoming call
Despite those entries, the user saw and heard no incoming-call alert on the iPhone.
The call remained unanswered and the iOS log then shows:
19:55:21.928 - Ringing call disappeared after 20 secs of ringing, cancelling
19:55:21.929 - Telling CallKit that call ended
The iOS Incident Report also reports:
- Background refresh mode: enabled
- CallKit throttled calls: 0
- CallKit denied calls: 0
- VoIP push token acquired
- IV and IS push subscriptions successful
iOS notification permissions for 3CX are enabled, including Lock Screen, Notification Center, Banners, Sounds, and Time Sensitive Notifications.
We also enabled "Also ring my mobile" on extension 1002 as a temporary safety net. During failed 3CX app calls, the separate cellular fallback call is generated successfully, confirming the inbound call is reaching the PBX and the fallback route is operating.
The key question is:
What could cause the 3CX iOS app to receive the VoIP PUSH and log that CallKit successfully presented the incoming call, while the iPhone provides no visible or audible incoming-call alert?
We have the complete PBX Verbose logs and the complete iOS Incident Report available if a 3CX staff member needs them. We have not posted the complete reports publicly because they contain identifiers/tokens and other information that should be kept private.
Please advise what we should check next or how we can provide the complete logs privately for analysis.
System:
- 3CX V20.0.1277 SP10
- Self-hosted
- 4SC / Free
- iOS app: 3CXPhone for iOS 20.0.22.153
- iPhone running iOS 26.6.1
- Extension 1002
- Incoming calls route through Ring Group 8001
- Ring Group ring time: 20 seconds
- No answer routes to voicemail
The problem is intermittent. Some calls ring the 3CX iOS app normally and can be answered, while other calls do not produce any visible or audible incoming-call alert on the iPhone and eventually route to voicemail.
We enabled Verbose logging on both the PBX and iOS app and reproduced the issue.
PBX evidence from an earlier failed controlled test:
- The PBX routed the call to extension 1002.
- The Mobile Client path returned SIP 180 Ringing.
- The Dialer path also returned SIP 180 Ringing.
- The extension route remained active for approximately 20 seconds and terminated due to timeout/no answer.
- The call then routed to voicemail.
We also captured a successful call for comparison. The initial PBX routing and 180 Ringing behavior was substantially the same, but on the successful call the actual iOS client subsequently connected as "3CXPhone for iOS 20.0.22.153".
We then reproduced another failure at approximately 19:55 EDT with iOS Verbose logging enabled.
For that failed call, the iOS Incident Report shows:
19:55:01.276 - Received push
19:55:01.278 - CallKit attempting to present incoming call
19:55:01.361 - CallKit presented the incoming call
Despite those entries, the user saw and heard no incoming-call alert on the iPhone.
The call remained unanswered and the iOS log then shows:
19:55:21.928 - Ringing call disappeared after 20 secs of ringing, cancelling
19:55:21.929 - Telling CallKit that call ended
The iOS Incident Report also reports:
- Background refresh mode: enabled
- CallKit throttled calls: 0
- CallKit denied calls: 0
- VoIP push token acquired
- IV and IS push subscriptions successful
iOS notification permissions for 3CX are enabled, including Lock Screen, Notification Center, Banners, Sounds, and Time Sensitive Notifications.
We also enabled "Also ring my mobile" on extension 1002 as a temporary safety net. During failed 3CX app calls, the separate cellular fallback call is generated successfully, confirming the inbound call is reaching the PBX and the fallback route is operating.
The key question is:
What could cause the 3CX iOS app to receive the VoIP PUSH and log that CallKit successfully presented the incoming call, while the iPhone provides no visible or audible incoming-call alert?
We have the complete PBX Verbose logs and the complete iOS Incident Report available if a 3CX staff member needs them. We have not posted the complete reports publicly because they contain identifiers/tokens and other information that should be kept private.
Please advise what we should check next or how we can provide the complete logs privately for analysis.
