Adding items

QBCore > shared > items.lua

letter = { name = 'letter', label = 'Letter', weight = 1000, type = 'item', image = 'letter.png', unique = false, useable = true, shouldClose = true, combinable = nil, description = 'Letter' }, 
sletter = { name = 'letter', label = 'Letter with Stamp', weight = 1000, type = 'item', image = 'sletter.png', unique = true, useable = true, shouldClose = true, combinable = nil, description = 'Letter with stamp' }, 
postboxkey = { name = 'postboxkey', label = 'Post Box Key', weight = 1000, type = 'item', image = 'postboxkey.png', unique = true, useable = true, shouldClose = true, combinable = nil, description = 'Post Box Key' },

ox_inventory > data > items.lua

['letter'] = {
	label = 'Letter',
},
['ssletter'] = {
	label = 'Letter With Stamp',
},
['postboxkey'] = {
	label = 'Postbox Key',
},