SIP trunks not registering on https://1299.3cx.cloud/

[melbourne]

Hello,

We have 2 customers on the above free version 3CX address, both customers SIP trunks are not registering.
The response from the service provider is as per below:

The trunk REGISTER is currently reaching us, we challenge for auth and the trunk sends the same REGISTER without auth. We receive the REGISTER, send a 401 back to the 3CX to challenge for auth and the same REGISTER (without auth) is sent so it is just looping.

Either:

1. The PBX is not currently configured to respond to 401 auth challenges
2. the 401 challenges aren't making it back/are being blacklisted by the 3CX

Can someone from 3CX assist us with this issue?

 

[NikosT_3CX]

@melbourne option 2 you mentioned is the case as option 1 is implemented on the PBX.
When the PBX sends out a Register with Sequence 1, you send 401 or 407 and the PBX does not
send out Register with Sequence 2 (keeps sending with Sequence 1 again) , this means that the trunk ip is Blacklisted on the PBX side. Check the Sequence numbers you receive.

 

[melbourne]

This is a free version; there is not much I can do from our side I believe.

 

[melbourne]

This is the fault when I run a test on the trunk:

Detected Issues

Registrar 'sip.melbournetelecom.com.au' is in Auto-discovery but does not resolve to any NAPTR or SRV records. Specify a SIP port to skip useless DNS lookups.
The SIP Registration attempt got a failure response [forced unregister] at 5/18/2026 7:16:14 PM +10:00

 

[melbourne]

Report as requested

<report level="Info">
<![CDATA[ Main trunk number '61391081222' Registrar sip.melbournetelecom.com.au has a DNS HOST record (sip.melbournetelecom.com.au) resolving to: [203.57.203.65] IP Mode: IPv4 Selected server address: 203.57.203.65:5060 Selected transport type: UDP Selected server domain: sip.melbournetelecom.com.au ]]>
</report>

<report level="Warning">
<![CDATA[ Registrar 'sip.melbournetelecom.com.au' is in Auto-discovery but does not resolve to any NAPTR or SRV records. Specify a SIP port to skip useless DNS lookups. ]]>
</report>

<report level="Error">
<![CDATA[ The SIP Registration attempt got a failure response [forced unregister] at 5/18/2026 7:16:14 PM +10:00 ]]>

 

[bitn2]

Is this a supported sip trunk for the free pbx? Which template did you use to configure the trunk?

 

[melbourne]

Yes, it is. VOCUS

 

[bitn2]

Which template did you use? Is this the standard or busines trunk?

 

[melbourne]

The problem has been resolved.
Thanks for your help.
I think 3CX had blacklisted