Need equipment help for Olympus C2500L

I bought the camera on EBay and it works great. Camera came with FL-40 flash. Seller warned me the flash will work on its on and camera flash works great but I can't use them together. Won't fire. I've went into the camera and made sure the curtain setting are the same on both but that doesn't work. Anyone have any suggestions I can try so I can save a trip to the repair shop? Any help would be appreciated. I have a degree in photography and worked in a camera shop for 5 years but that was back in the day.