This should be so simple! I can't get 3CXPhone for Android to register to my 3CX server. The log says Code: 15:11:58.281 [CM102001]: Authentication failed for SipReq: REGISTER 188.8.131.52 tid=PjDkwfZ1BQdgOgIAGyCCob3QODhf.E8ksH cseq=REGISTER firstname.lastname@example.org:5060 / 11540 from(wire); Reason: Credentials don't match, check that authorization-ID and password match the ones in extension settings 15:11:58.281 [CM502001]: Source info: From: <sip:email@example.com>;tag=cy6uuPetfQksunavREy8QALsoiIDSeju; To: <sip:firstname.lastname@example.org> 15:11:58.281 [CM302002]: Authentication failed due to unidentified source of: SipReq: REGISTER 184.108.40.206 tid=PjDkwfZ1BQdgOgIAGyCCob3QODhf.E8ksH cseq=REGISTER email@example.com:5060 / 11540 from(wire) I'm 100% certain I have the authentication ID and password correct. I've set up a bunch of other extensions on this 3CX, I am familiar with what these are. I can get SIPDroid to register to the same extension with no problem using the same credentials. Code: 15:01:08.390 [CM504002]: Ext.107: a contact is unregistered. Contact(s):  15:00:27.359 [CM504001]: Ext.107: new contact is registered. Contact(s): [sip:firstname.lastname@example.org:48485;transport=tcp/107] I've typed them in 5 times (looking at each character in the invisible password as it is entered). Can anyone see anything in the above 1st set of log lines that might help me?