ERR_CONNECTION_REFUSED when running packet_sender.exe after npm run dev

[ariadnatp]

Every time I try to run packet_sender.exe after launching the frontend with npm run dev, the GUI shows ERR_CONNECTION_REFUSED.
However, this does not happen when I run the backend instead, everything works fine in that case.

I also tried restarting my computer and running only the frontend with the packet sender (without the backend), but I get a "failed to fetch" error.