Ran into the same issue. Have you checked which version of node you have installed?
At the time of writing the docs say that node version must be:
8 < version < 14.15.5
I had v16 installed, which resulted in the ‘cannot get /’ error.
To get around this I uninstalled node completely and installed nvm (GitHub - coreybutler/nvm-windows: A node.js version management utility for Windows. Ironically written in Go.). On windows with nvm, you install multiple versions of node and easily switch between them. For the latest verson (so you stay up to date for other purposes):
nvm install latest
To install the latest version compatable with the remote control web interface:
nvm install 14.15.5
To use this version:
nvm use 14.15.5
To test that node is running correctly
node -v
Which should return:
v14.15.5
Next, uninstall the remote control web interface plugin from epic launcher. Navigate to:
C:\Program Files\Epic Games\UE_4.26\Engine\Plugins\Marketplace
And delete the ‘RemoteControlWebInterface’ directory.
Head back to epic and install the web interface once more. Boot up your project and it should rebuild the depndencies once again (this time using the supported version of node).
Worked for me, hope that helps you!