How to disable notification sound in Facebook application

I have the Facebook application installed and I can't seem to figure out how to turn off the (really loud and sharp) notifications sound, what I tried so far was 1. go to Settings > App Settings > Sounds in the App and untick the option 2. go to Settings > Notifications Settings but I couldn't find a relevant setting I don't want to mute or lower the device volume because I have other apps with notifications that are actually important for me, I use a OnePlus2 with Oxygen3.6.1 if it helps