"Config file "edair_mod_inventory.json" located in:
C:\Users\%username%\AppData\LocalLow\Magnum Scriptum Ltd\Quasimorph"

I can't seem to get this to work.

{
"bp_slots_flat": 0,
"bp_slots_mult": 4.0,
"bp_weight_flat": 70,
"vest_slots_flat": 0,
"vest_slots_mult": 4.0,
"satiety_kg": 100
}

Maybe the values are too high for the slots_mult?

All of the values are fine. Does the mod work at all? Did it work before changing the values?
If you delete config file and restart the game is config recreated?
Also if you can please upload Player.log file somewhere (it is in the same folder as config) it would be helpful.

It was a steam sync issue on my end , restarting steam and ignoring the sync error (also turning off steam cloud saving) has seemingly fixed the issue. (Edit: you also have to remove and replace the item to get it to update to the new size) Thank you for your help.

Edit: I did some more testing, to answer your questions; The mod works for backpacks but not vests, I am currently using Rookie, with 6 slots, Pathfinder also has 6 slots. Seemingly there is a max of 6 slots.

I'll see about uploading the Player.log at some point if I can't fix it myself.
Thanks again!

This is correct, that is intended behaviour. For the vest there is limit of 6 slots, and after changing settings you have to remove and equip item for it to update.
I should probably include that in mod description.

does it work with 8.5?

in 8.6

Total 1 loaded. Mods list:
Mod edair_mod_inventory loaded.
Actors loaded, process took 1.13 seconds.
Unexpected error in hook AfterConfigsLoaded for mod edair_mod_inventory: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.MissingMethodException: Method not found: MGSC.ConsoleDaemon MGSC.ConsoleDaemon.get_Instance()
at (wrapper managed-to-native) System.Object.__icall_wrapper_mono_gc_wbarrier_generic_nostore_internal(intptr)
at (wrapper write-barrier) System.Object.wbarrier_conc(intptr)
at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0006a] in <31687ccd371e4dc6b0c23a1317cf9474>:0
--- End of inner exception stack trace ---

Updated to latest version.