Android gateway troubleshooting: detection, sleep, delivery
Twelve symptoms with their usual causes and fixes, the order to check them in, and the keep-alive checklist that prevents the most common one: a phone that quietly goes to sleep on the job.
Check in this order
Each step has an expected result; stop at the first one that fails.
Same network
Confirm the PC and the phone are on the same LAN (or the VPN is up). Expected: both show addresses in the same subnet.
Reachable address
Open the phone's IP and port in a PC browser. Expected: the app's panel loads. If it does not, the problem is network, not software.
Default SMS app
Check the app still holds the default SMS role. Expected: it does; without it, inbound replies never reach the gateway.
Battery optimisation excluded
Exclude the app from battery optimisation and any vendor “deep sleep” list. Expected: the app survives the night with the screen off.
Firewall and port
Let the desktop app through the PC firewall and confirm the port matches the app's panel. Expected: the device shows online in SMS Deliverer.
Test send
Send one message to your own number. Expected: it leaves the phone in seconds and the report updates. If it fails here, the cause is the SIM or the carrier, not the link.
The twelve-row fault table
| # | Symptom | Usual cause | Fix |
|---|---|---|---|
| 1 | Connection refused | Different subnet or guest Wi-Fi isolation | Same network for both devices; disable AP isolation on the router |
| 2 | Panel unreachable after a router reboot | DHCP handed the phone a new IP | Reserve a fixed IP for the phone; re-add the device |
| 3 | Browser reaches the panel, the app does not | PC firewall blocks the desktop app | Allow SMS Deliverer in the firewall for private networks |
| 4 | Device added but never online | Wrong port entered | Read the port from the app's panel again; do not guess 8080 |
| 5 | App stops sending at night | Battery optimisation kills it | Exclude the app; keep the charger connected |
| 6 | App dies in the background within hours | Vendor battery manager (aggressive OEM power saving) | Add the app to the vendor's protected/never-sleep list; keep the phone on power |
| 7 | Sends work, replies never arrive | App is not the default SMS app | Restore the default SMS role in Android settings |
| 8 | Messages stuck in the queue | Phone offline, or SIM absent/deactivated | Check the device state, then the SIM in the phone itself with a manual SMS |
| 9 | SMS fine, MMS fails | Carrier MMS settings or policy | Confirm MMS works manually on the phone first; see the MMS page for size limits |
| 10 | No delivery reports | Carrier does not return them, or reports not requested | Enable report requests; accept that some carriers never send them |
| 11 | No signal where the phone sits | Position or band coverage | Move the phone near a window; check the carrier's coverage map |
| 12 | Works over VPN but with timeouts | Latency and tunnel drops | Keep the phone on the LAN where possible; if VPN is required, expect slower polls |
The keep-alive checklist
- Charger connected permanently; a gateway phone is infrastructure, not a handset.
- App excluded from battery optimisation and from the vendor's deep-sleep list.
- Wi-Fi set to stay connected during sleep (Android's Wi-Fi sleep policy).
- Fixed IP reserved in the router, so the PC never loses the address.
- Screen lock and timeout can stay as they are; they do not stop the app once optimisation is off.
- After a reboot, open the app once: whether it restarts itself varies by Android build and is not verified by us.
When it is the carrier, not the app
If the manual test SMS from the phone's own messaging app also fails, the link is fine and the SIM or the carrier is the problem: credit exhausted, plan changed, or the number blocked for machine-like sending. No gateway setting fixes that; the carrier does. For the sending limits that lead there, see rate limits.
This guide is part of the Android gateway cluster: overview, multi-SIM, rate limits, troubleshooting.
Questions about gateway faults
The PC says the phone is not detected. Where do I start?
Open the phone's IP and port in a PC browser on the same network. If the panel does not load, it is a network problem: subnet, guest isolation or a changed IP. If it loads, check the firewall and the port you entered.
Why does the app stop sending overnight?
Battery optimisation. Android and vendor power managers suspend background apps; exclude the gateway app from both and keep the phone on its charger. This is the single most common cause of missed messages.
Why do outbound messages work but replies never arrive?
The app lost the default SMS role. Android only delivers inbound SMS to the default messaging app, so restore that role in the phone's settings.
Do I need to keep the screen on?
No. Once battery optimisation is excluded and the phone is on power, the screen can lock and turn off; the app keeps running.
What if a manual SMS from the phone itself also fails?
Then the problem is the SIM or the carrier, not the gateway: check credit and plan status, and if the number was blocked for bulk sending, only the carrier can restore it.