CWD Not sure if you have taken this screen shots from IOS 15 solution guide but I have seen this scenario for third party SIP phones and when we have Digest Credentials enable. So whenever Digest credentials comes into the picture UAS (SIP Server) rejects the first register message from UAC as per RFC guide [RFC3261] Basically UAS is challenging the authenticity of the register messages and in the second register message Digest user creds and MD5 algorithm is exchanged. You can try decoding the first register and second register message you will see the difference and it seems to be as per SIP RFC. This is working as design when you enable the authorization. In order to make it work your provider need to be aware of the same which is not quite easy here in case of provider.
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