Answer those, please:
-Are you running GameLauncher.exe ? If not, what .exe files are you running?
-When you open new tab in browser and go to http://127.0.0.1:8188/ in browser does the comfy interface open?
-Is the command line window with ComfyUI open?
-Is only one command line window with Comfy open?
-When you get 400 error and than close dialogue window in the game, if you go to command line window with comfyUI and press "Enter" in it one time, than go back to the game and try image generation again, does the problem persist?
-Are you running everything as administrator?
-Anything peculiar in any cmd windows?
-Do you run any security software?