android app reporting an error

I am a total newbee to traccar... this afternoon, I installed traccar server on a Raspberry Pi 4. Updated the port forwarding for port 5055.
Server runs.
Then instaled traccar client on Android phone. Entered the URL.
In the server gui, added the device using the device ID.
After some playing around, I can see the device on the server map. So: looks OK....
But when I look at the status overview on the client, it keeps telling me: "verzenden mislukt", which in English would be "transmission failed".
What is going wrong?

Have you followed the troubleshooting guide?

Sorry, newbee... where is that guide? :-(

OK, found the guide.
The Android client reports the send error. But the strange thing is that the server shows that the client reports OK! I can also see the entries in the log
file. So it seems to be OK, but nevertheless the errors keep showing in the client status screen!

2024-12-02 12:18:03  INFO: [T9fc60ab7] connected
2024-12-02 12:18:03  INFO: [T9fc60ab7: osmand < 10.0.0.191] POST /?id=305534&timestamp=1733122566&lat=52.0895009&lon=5.0427327&speed=0.0&bearing=0.0&altitude=47.0&accuracy=19.9270000457763>
2024-12-02 12:18:03  INFO: [T9fc60ab7] id: 305534, time: 2024-12-02 07:56:06, lat: 52.08950, lon: 5.04273, course: 0.0, accuracy: 19.9
2024-12-02 12:18:03  INFO: [T9fc60ab7: osmand > 10.0.0.191] HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n

Are you sure it's not from another device?

Yes. At the Android side, the traccar app only has a single device by nature. On the server side, I've added only one device.
The strange thing is that in spite of the errors, the server actualy "sees" my phone!

One thing is strange. When I look at the map on the server screen and "replay" my movements, it goes as far as 09:15 this morning.
When I look at the latest entry in the log, I see the timestamp of the logrecord is different from the timestamp in the data!

2024-12-02 16:52:57  INFO: [T867d1954] connected
2024-12-02 16:52:57  INFO: [T867d1954: osmand < 10.0.0.191] POST /?id=305534&timestamp=1733127318&lat=52.091752&lon=5.0419255&speed=0.0&bearing=0.0&altitude=46.5999984741210>
2024-12-02 16:52:57  INFO: [T867d1954] id: 305534, time: 2024-12-02 09:15:18, lat: 52.09175, lon: 5.04193, course: 0.0, accuracy: 100.0
2024-12-02 16:52:57  INFO: [T867d1954: osmand > 10.0.0.191] HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n

Try connecting from a different network. Maybe some communication is blocked.

I tried disconnecting the phone from my LAN, so it runs on the 4G connection only. No change.

Logs?

you mean the log on the server?

here are some entries:

2024-12-02 20:31:30  INFO: [Taef8ed18: osmand < 89.205.137.114] POST /?id=305534&timestamp=1733129718&lat=52.091752&lon=5.0419255&speed=0.0&bearing=0.0&altitude=46.599998474121094&accur>
2024-12-02 20:31:30  INFO: [Taef8ed18] id: 305534, time: 2024-12-02 09:55:18, lat: 52.09175, lon: 5.04193, course: 0.0, accuracy: 100.0
2024-12-02 20:31:30  INFO: [Taef8ed18: osmand > 89.205.137.114] HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n
2024-12-02 20:36:30  INFO: [Taef8ed18] disconnected
2024-12-02 20:40:05  INFO: [T0b0cd744] connected
2024-12-02 20:40:05  INFO: [T0b0cd744: osmand < 89.205.137.114] POST /?id=305534&timestamp=1733129864&lat=52.0917505&lon=5.041918&speed=0.0&bearing=0.0&altitude=46.599998474121094&accur>
2024-12-02 20:40:05  INFO: [T0b0cd744] id: 305534, time: 2024-12-02 09:57:44, lat: 52.09175, lon: 5.04192, course: 0.0, accuracy: 100.0
2024-12-02 20:40:05  INFO: [T0b0cd744: osmand > 89.205.137.114] HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n
2024-12-02 20:45:05  INFO: [T0b0cd744] disconnected
2024-12-02 20:48:40  INFO: [Tdcb5e889] connected
2024-12-02 20:48:40  INFO: [Tdcb5e889: osmand < 89.205.137.114] POST /?id=305534&timestamp=1733129924&lat=52.0917505&lon=5.041918&speed=0.0&bearing=0.0&altitude=46.599998474121094&accur>
2024-12-02 20:48:40  INFO: [Tdcb5e889] id: 305534, time: 2024-12-02 09:58:44, lat: 52.09175, lon: 5.04192, course: 0.0, accuracy: 100.0
2024-12-02 20:48:40  INFO: [Tdcb5e889: osmand > 89.205.137.114] HTTP/1.1 200 OK\r\ncontent-length: 0\r\n\r\n
2024-12-02 20:50:03  INFO: user: 1, action: login, from: 10.0.0.7

these entries were triggered from a phone without Wifi connection, so outside of my LAN.

OK, no idea what's going on.

when I look at the entries in the server logfile, it looks like the triggers come in several hours later! The timestamp in the data looks like the time the trigger originated. The timestamp of the record shows the time it was file in the server. Correct?

Getting closer. After re-installing the client on my Android phone, and in particular paying attention to the app setting, it now works.
Except.....
When I am off my own LAN (Wifi off), it works just great. When I am on my LAN (Wifi on), it fails to send updates.
So I tried changing my DNS name into hard coded internal address of the server, and switch Wifi on, it will work. The probles seems to be in the translation of the URL by a DNS server... does this make sense, or is it nonsense?

Does your DNS resolve to the internal address?