Hello,
Once you send "admin01 uci set network.lan.ipaddr=10.77.20.1" SMS command to the router, router should respond with "Replaced existing value network.lan.ipaddr=10.77.20.1" SMS message.
Do you receive such SMS messages from the router? If no, then your router does not accept/recognize the SMS command.
To begin with, check for any typing errors, which might occurred by accident (e.g. incorrect password, missing space between password/command/parameter etc).
If SMS command is indeed correct, would you be able to send one more "uci set" command to the router, then download troubleshoot package from the router and upload it here? (Troubleshoot package can be downloaded from "System -> Administration -> Troubleshoot" menu)
Note: Troubleshoot package contains router's configuration information and current router's logs. All passwords and certificate information is hidden automatically (not included in troubleshoot package). Nonetheless, it is recommended to remove any other information (e.g. phone numbers) that you might not want to share publicly.