Have a look in FMOD > Log Viewer. It will tell you what plugin you are missing.
Most likely it is the FMOD Distance Filter or FMOD Gain. These plugins aren’t included in the Unity integration package.
To fix this, in FMOD’s (the app) folder there will be these two plguins’ DLL files. Copy these into Assests/Plugins/x86_64 and in FMOD’s settings, click ‘Add Plugin’ and add the name of the plugin without the .dll. It should look like ‘fmod_distance_filter’ rather than ‘FMOD Distance Filter’ as you’re copying the name of the file, not what it is when looking pretty.
Hopefully that will fix your error! Just reply if you’re unsure on something.