Ah… all right

that’s already something now:

403: Forbidden
Unauthorized IP Address.

Either disable the IP address whitelist or add your address to it.

If you’re editing settings.json, see the ‘rpc-whitelist’ and ‘rpc-whitelist-enabled’ entries.

If you’re still using ACLs, use a whitelist instead. See the transmission-daemon manpage for details.

Whitelisting 192.168.178.* doesn’t seem to help though.