do yourself a favor and lookup facebook threads in this forum.
There are multiple different issues, and depends on which OBS Studio version you are using, and exactly which issue you are having (not working isn't sufficiently descriptive)... l/live/preview not working is a known facebook back-end issue - contact facebook, or research the work-arounds to FB web page code issues. Being unable to stream (red light, not green) to FB at all... depends on OBS Studio version.
