nano /etc/ups/upsd.users

[monuser]
                password = secret
                upsmon master
    actions = SET
    instcmds = ALL


synosystemctl restart ups-usb


sh-4.4# telnet localhost 3493
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
USERNAME monuser
OK
PASSWORD secret
OK
INSTCMD ups beeper.disable
OK
SET VAR ups input.transfer.low "160"
OK
SET VAR ups input.transfer.low "151"
OK