A SIP AT0 Trunk Fails to Be Registered with the IMS.
Check whether the registered account and password are correct.
Check the format of the To header field on the SIP AT0 trunk. During registration, number regulation is enabled for SIP registration messages by default. The format of the To header field is Invite "3001;phone-context=+86755@huawei". The IMS may not support this format.
Run the number-parameter 27 0 command in the SIP AT0 trunk view to set parameter 27 to 0. If parameter 27 is set to 0, number regulation is disabled.