well, i changed the config file directory to a new directory i made on the usb drive. (so that i can find the config and see if the daemon created it)
the RPC URL is the same as yours (the default)
my RPC config section is like this
RPC enabled tick
RPC port 9091 ( suppose this can be anything unused)
RPC bind address 192.168.1.1 (router local ip)
RPC url /transmission (this is the default)
RPC whitelist enabled tick
RPC whitelist 127.0.0.1, 192.168.star.star
RPC auth required unticked
i would also try to reboot ( i know linux does not need to have rebooted, but still, might work)