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Not registering: on-screen messages and error codes

What 401, 403, 404, 408, 423, 503, “No Service”, “Register Failed”, “Not registered” mean — plain-language causes and what to check

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Phone not registering: on-screen messages and error codes

Registration is the phone telling the PBX every few minutes: “I am such-and-such extension, call me here.” The server answers with a short code, and the phone shows it in its own way: one brand writes “Register Failed”, another draws a grey icon, a third says “Device not registered” into the handset. The cause is almost always in one of the five fields from the “Extension credentials” window or in the venue network — and the code lets you name it precisely instead of trying everything in turn.

How to set up a phone from scratch is in the overview “SIP Phone Setup”; if the phone is registered and the trouble is something else — troubleshooting by symptom.

Check the admin panel first#

Admin panel → Telephony → “Staff & groups”:

  1. The dot next to the extension. “Connection not checked yet” — the phone never got as far as registering: address, login or network. “No connection” — it registered and dropped off: network, router, or someone reset the password. “Turned off” — the operator is switched off in the admin panel itself; the phone has nothing to do with it. The status refreshes about once a minute.
  2. The “Extension credentials” window — compare the server and the login with what is in the phone. The password cannot be viewed (we store only its hash): if in doubt, click “Reset password” and enter the new one.
  3. “Connections” in the device card (click the tag in the extension row): when the last successful registration was, from which address and which network. A “PBX restarted” mark means every phone dropped off at once at that moment, and it is not a device fault. An address from a foreign country or another provider means an outsider is registering with this login: reset the password.
  4. The SIP trace on a dedicated PBX (“Server” tab → “Wire diagnostics”): start a capture and reboot the phone — the transcript will show its REGISTER and the PBX’s answer with a code.
  5. Once the phone registers, dial *43 straight away: registration and audio break separately, and the green dot says nothing about audio (how to read the result).

How registration works#

Four steps, and the first rejection in them is normal:

  1. The phone sends a REGISTER request: “I am sip-…-101, call me here.”
  2. The PBX answers 401 — “identify yourself” — and sends a one-time challenge. This is not an error: every registration starts this way.
  3. The phone repeats the request with an answer to the challenge computed from the password. The password itself never travels over the network.
  4. The PBX answers 200 OK and names a period. Before it expires, the phone registers again by itself.

If step 4 brings another 401 instead of 200, the login or password was not accepted. If there is no answer at all, the request never reached the PBX or the answer never came back.

For the network administrator: periods, checks and NAT on the PBX side
  • Registration period. A phone may ask for 60 to 3600 seconds. Less than 60 — the PBX answers 423 Interval Too Brief; more than 3600 — it cuts it to 3600; no period given — the PBX sets 120 seconds.
  • Device checks. Every 60 seconds the PBX asks each registered device “are you there?” (SIP OPTIONS) and waits 3 seconds for an answer. No answer — the dot goes out, and calls are not sent to that device until it reappears.
  • Devices per account. Up to 5 at a time by default; the sixth registration pushes out the oldest. On a dedicated PBX both values can be changed in “Advanced SIP settings”.
  • Transport. UDP and TCP on port 5060. The platform does not currently offer TLS for phones — a phone set to TLS will not register.
  • NAT. The PBX itself replies to the address and port the request actually came from and remembers that one, not the address the phone claims. STUN and “NAT traversal” in the phone are not needed.

Values come from shared/sip/advanced-options.json (the registration and nat groups).

Server response codes#

You can see the code in the SIP trace, in the account status in the phone’s web interface and in a softphone’s log. If your phone only shows “Register Failed”, see the next section.

Code What it means in plain words What to check
401 / 407 once, then 200 A normal two-step registration Nothing
401 over and over The login or password was not accepted. On our PBX a wrong login and a wrong password look the same — the server does not hint which one is wrong, so that scanners cannot enumerate existing extensions ⚠️ verify The login in full sip-…-<number> in both fields (User Name and Auth Name); the password from after the last “Reset password”; no trailing space after copying
403 Forbidden The server recognised you and refused. Our PBX answers a wrong password with 401, so 403 more often means “you are knocking on the wrong door”: the phone holds the address of a previous provider or someone else’s PBX. Another case — the account has run out of device slots while pushing out old ones is turned off in “Advanced SIP settings” The server address — copied from the admin window; the previous owner’s provisioning server is cleared; the number of devices on the account in the card
404 Not Found This server has no such account or domain A typo in the server address; something of its own typed into the phone’s Domain / Realm field; the shared server address used at a venue with a dedicated PBX
408 Request Timeout, or no answer at all The request did not reach the PBX or the answer did not come back to the phone Server address, port 5060, transport UDP (not TCP / TLS); SIP ALG on the router; outbound UDP 5060 blocked; the phone on guest Wi-Fi
423 Interval Too Brief The phone asks for too short a registration period: our minimum is 60 seconds The Expires / Register Expiration / Registration Period field — at least 60; the factory value needs no change
488 / 606 Not about registration: this is how a call is answered when the sides could not agree on a codec At least one of G.711 (PCMA, PCMU) or G.722 must be enabled in the phone — see “No audio”
503 Service Unavailable The server is temporarily not accepting. It happens while the PBX restarts for an update — “Connections” will show a “PBX restarted” mark. Some apps also show 503 when they could not even send the request Wait a couple of minutes and reboot the phone; if it persists — contact support

On-screen messages#

The same cause looks different on different brands. What devices display, according to the manufacturers’ documentation:

Brand What you see What it means More
Yealink T “No Service” The phone has no working account: the line is off or did not register Yealink T
Yealink T “Register Failed”, a grey line icon The server refused — login or password Yealink T
Yealink T “Unregistered” The account was deregistered: the line was switched off or the phone logged out Yealink T
Yealink W (DECT) “Unregistered!” on the handset The handset is not paired with the base — radio, not the PBX Pairing handsets
Grandstream GRP “Unregistered” on the line The account is not registered; a common cause is Account Active: No Grandstream GRP
Grandstream HT (gateway) A voice saying “Device not registered” when the handset is lifted The gateway port is not registered Grandstream HT
Grandstream DP (DECT) “SIP Registration: NO” on a red background in the base status The base account is not registered Grandstream DP
Fanvil Line Status “Trying”, then “Timeout” The server does not answer or answers with a refusal — login, address, network Fanvil
Panasonic KX-TGP600 “Error:003” on the handset; an empty VoIP Status in the web interface Registration with the server failed; an empty status also appears on an authentication error Panasonic
Snom An empty square instead of the handset icon The phone is configured, but the server does not answer Snom
Zoiper “Not registered” in the account status Registration failed; details behind the “!” icon at the bottom of the window Softphones: Zoiper errors

Any softphone that complains about DNS (“address not found”) is saying one thing: the server address has a typo, or the device cannot reach DNS (UDP 53).

Special cases#

A wrong password does not block your address#

Many PBXs block the source address after a few failed attempts. Ours does not, and this is deliberate: all the venue’s phones sit behind one address, and a single device with an old password would cut off the whole dining room. So a failed attempt carries no “penalty”: fix the password and the phone registers on its very next attempt, with no unblocking to wait for.

The PBX does count rejections, though. On a dedicated PBX, if about 300 rejections arrive from one address within 5 minutes, or someone is trying non-existent extensions, the owner gets a message in the work chat — that is what an internet scanner looks like, not your own office. Whether to block the address is a human decision.

Teams or Zoom firmware#

Yealink, Poly, AudioCodes and Cisco sell the same models with firmware for Microsoft Teams, Skype for Business or Zoom. From the outside it is the same device, but you cannot enter an ordinary SIP account into it: there is no Account tab or SIP server field at all, and the boot screen shows a Teams or Zoom logo. Such a phone will not connect to our PBX until the manufacturer’s SIP firmware is loaded on it (it does not exist for every model). Details per brand — Yealink T, Poly, Cisco.

A second-hand phone “brings back” old settings#

You set it up, everything worked — next morning it will not register again, and a foreign server sits in the fields. The previous operator’s provisioning server address is still inside, and the phone downloads its configuration from there on every reboot. Clear the provisioning address (each brand keeps it in its own place — see the brand page) or do a factory reset.

Grandstream waits 20 minutes after an error#

After a 403 Forbidden answer, Grandstream phones and gateways by default retry registration only after 1200 seconds (the Registration Retry Wait Time upon 403 Forbidden field). Once you have fixed the address or the login, reboot the device — otherwise it will honestly keep quiet for another 20 minutes.

Registers, then drops off a minute or two later#

The dot flips between green and grey, and “Uptime” shows frequent gaps. Registration reaches the PBX, but the router closes the way back before the phone refreshes it. The cure is keep-alive in the phone and SIP ALG switched off — see “Incoming calls only work for the first minutes”.

What to do, step by step#

After each step, wait a minute and look at the dot in the admin panel; go further only if it did not help.

  1. The login in full — sip-…-<number> in User Name and in Auth Name / Register Name / Authentication ID. Not “101”.
  2. A new password. Click “Reset password” in the admin panel, copy the new one with the button and enter it again — do not guess the old one.
  3. The server address — copied from the “Extension credentials” window, without http://, without spaces and without a port after a colon.
  4. Port 5060, transport UDP. TLS and SRTP are off in the phone.
  5. The line is enabled — Line Active, Account Active, Activate, Register: Yes — and the settings are saved (Save / Apply / Confirm).
  6. Reboot the phone. Especially Grandstream after a 403 and Snom after changing the account.
  7. Network. The phone is on the staff network, preferably by cable; SIP ALG is off on the router; outbound UDP 5060 is open. Details — “Network, router and internet”.
  8. Someone else’s provisioning — clear the address or reset the phone.
  9. Firmware — SIP, not Teams / Zoom.

What to send to support#

  • the phone’s model and firmware (the string from the equipment tag if it ever registered, or from the phone’s own Status screen);
  • the exact message on the screen or the code from the account status — a photo of the screen is best;
  • the extension and the time of the last attempt;
  • a screenshot of the account page in the phone’s web interface (cover the password);
  • on a dedicated PBX — the SIP trace text from the moment the phone rebooted;
  • how the phone is connected (cable / Wi-Fi) and the router model.

How to reach us — “Support”.

Frequently asked questions#

The password is definitely right, but the phone says Register Failed — why?#

Most often it is the login, not the password: the second field (Auth Name, Authentication ID, Register Name) still says “101” or is empty. The second suspect: someone clicked “Reset password” for this extension, and the old password no longer works. The third: an invisible trailing space after copying. Do not try variants: reset the password and enter the new one in both required fields.

We got a message saying someone is guessing account names on our PBX — have we been hacked?#

No, that is internet background noise: scanners try port 5060 of every server around the clock. The message means the PBX noticed it and let nothing in. Our passwords are long and generated by the system — they cannot be guessed by brute force. If the address in such a message is your own venue’s, it is your own phone with an old password: find it in “Connections” and enter the new password.

How many phones can be registered on one extension?#

Up to five at a time by default — for example, a desk phone and a smartphone app; an incoming call rings on all of them at once. A sixth pushes out the oldest, and that one stops receiving incoming calls. If different people need to be rung, that is a ring group, not a shared login.

Why did the phone register only 20 minutes after the fix?#

The phone decides for itself when to try again. Grandstream waits 1200 seconds after a 403 rejection, other brands from 20 seconds to a few minutes. After any change to the account, reboot the device — it is the fastest way to see the result.

Sources#

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