You missed the point of both messages.
If you configure a monitor session on the data switch against the STMI port, or install Wireshark on the PC with the softclient, what does the lan capture tell you is happening? SIP subscriber only needs to know its station number and registration IP address to work, unless you configure security/digest authentication. So you should see a register attempt and then a response from the STMI.
plokijuh mentions the opttbl, which if you have never had any SIP subscribers, or done anything with ISDN BRI, is likely to not be initialised. Make a dis-zand

pttbl; to check current config. If it's empty, it will need a cha-zand

ptload like plokijuh mentions, because for SBCSU S0PP SIP stations, the ISDN tables are used for protocol conversion from SIP. After the optload you can make a dis-zand

pttbl; again to see the difference.