You have to keep RHMAC open in order to work.
As I tried it first through the game and it didn't work, I ended up checking if it could be done through Content Manager (But I think it didn't work because RHMAC wasn't open ).
Set up via Content Manager (after pasting the dlls, py and exe).
Settings > Content Manager > Drive
-- Check the checkbox "RHM integration"
-- And the path to the "RealHeadMotionAssettoCorsa.exe" (This will execute the RHMAC when you click "Go!")"
Amazing mod! Thank you!