Hi Henning, I’m a numbskull – I was editing the wrong config file. Thanks for your help! Jawaid From: Henning Westerholt &lt;hw(a)gilawa.com&gt; Date: Friday, November 17, 2023 at 3:01 AM To: SRList SRList via sr-users &lt;sr-users(a)lists.kamailio.org&gt; Cc: Jawaid Bazyar &lt;bazyar(a)gmail.com&gt; Subject: RE: auth_check : sip user / authentication user mismatch Hello, according to the module docs it should be: if (!auth_check("$fd", "subscriber", “0”)) { // default 1, change to 0 to skip check You missed some quotes in your example below. Please give it a try. Cheers, Henning From: Jawaid Bazyar via sr-users &lt;sr-users(a)lists.kamailio.org&gt; Sent: Donnerstag, 16. November 2023 22:37 To: SRList SRList via sr-users &lt;sr-users(a)lists.kamailio.org&gt; Cc: Jawaid Bazyar &lt;bazyar(a)gmail.com&gt; Subject: [SR-Users] auth_check : sip user / authentication user mismatch Hi, I am trying to register an endpoint as follows: REGISTER sip:siptest.booger.net SIP/2.0 Via: SIP/2.0/UDP X.X.X.X.76:31114;branch=z9hG4bK223420485;rport From: sip:1720XXXXXXX@siptest.booger.net;tag=962873337 To: sip:1720XXXXXXX@siptest.booger.net Call-ID: 2053687751-32761-1(a)EH.BJI.BAE.HG CSeq: 2067 REGISTER Contact: sip:1720XXXXXXX@X.X.X.X:31114;reg-id=2;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000B82A1C58B>" Authorization: Digest username="654fe87c-67ff-42dd-8d5e-79786a99713c", realm="siptest.booger.net", nonce="ZVaJtmVWiIrsuWc5hkzM3MUUUs8MgRFR", uri=sip:siptest.booger.net, response="119a3b6426cdcfa037bf1825b69139a5", algorithm=MD5 X-Grandstream-PBX: true Max-Forwards: 70 User-Agent: Grandstream GXP2170 1.0.11.64 Supported: path Expires: 120 MAC: 00:0b:82:a1:c5:8b Allow: INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, INFO, REFER, UPDATE, MESSAGE Content-Length: 0 Note that the Authorization username differs from the To-From username. This is intentional, as I am testing use of randomly generated credential . This worked with this endpoint directly against Asterisk, for instance. However, registering against Kamailio now, I am getting: Nov 16 21:24:26 vs-rs01 /usr/sbin/kamailio[584855]: DEBUG: {1 2067 REGISTER 2053687751-32761-1(a)EH.BJI.BAE.HG} auth_db [authorize.c:503]: auth_check(): authentication username mismatch with from/to username Even though I have this set in the config: if (!auth_check("$fd", "subscriber", 0)) { // default 1, change to 0 to skip check 0 is supposed to mean no user checks performed. I am doing this because I want to use the complex credentials for authentication, but want the endpoint to tell me the phone number in an INVITE to/from, instead of putting in the extremely long credential. Is there a way to get Kamailio to accept different SIP User ID and Authentication ID fields? Thanks, Jawaid