diff --git a/imports/callback/client.lua b/imports/callback/client.lua
index aaafb90..6535bda 100644
--- a/imports/callback/client.lua
+++ b/imports/callback/client.lua
@@ -11,7 +11,7 @@ RegisterNetEvent(cbEvent:format(cache.resource), function(key, ...)
 end)
 
 ---@param event string
----@param delay number | false prevent the event from being called for the given time
+---@param delay? number | false prevent the event from being called for the given time
 local function eventTimer(event, delay)
     if delay and type(delay) == 'number' and delay > 0 then
         local time = GetGameTimer()
@@ -28,8 +28,8 @@ end
 
 ---@param _ any
 ---@param event string
----@param delay number | false
----@param cb function|false
+---@param delay number | false | nil
+---@param cb function | false
 ---@param ... any
 ---@return ...
 local function triggerServerCallback(_, event, delay, cb, ...)
@@ -67,12 +67,19 @@ end
 
 ---@overload fun(event: string, delay: number | false, cb: function, ...)
 lib.callback = setmetatable({}, {
-    __call = triggerServerCallback
+    __call = function(_, event, delay, cb, ...)
+        local cbType = type(cb)
+
+        assert(cbType == 'function', ("expected argument 3 to have type 'function' (received %s)"):format(cbType))
+
+        return triggerServerCallback(_, event, delay, cb, ...)
+    end
 })
 
 ---@param event string
 ---@param delay? number | false prevent the event from being called for the given time.
 ---Sends an event to the server and halts the current thread until a response is returned.
+---@diagnostic disable-next-line: duplicate-set-field
 function lib.callback.await(event, delay, ...)
     return triggerServerCallback(nil, event, delay, false, ...)
 end
@@ -94,7 +101,8 @@ local pcall = pcall
 
 ---@param name string
 ---@param cb function
---- Registers an event handler and callback function to respond to server requests.
+---Registers an event handler and callback function to respond to server requests.
+---@diagnostic disable-next-line: duplicate-set-field
 function lib.callback.register(name, cb)
     RegisterNetEvent(cbEvent:format(name), function(resource, key, ...)
         TriggerServerEvent(cbEvent:format(resource), key, callbackResponse(pcall(cb, ...)))
diff --git a/imports/callback/server.lua b/imports/callback/server.lua
index 718cc07..65eef3e 100644
--- a/imports/callback/server.lua
+++ b/imports/callback/server.lua
@@ -3,10 +3,10 @@ local cbEvent = '__ox_cb_%s'
 local callbackTimeout = GetConvarInt('ox:callbackTimeout', 300000)
 
 RegisterNetEvent(cbEvent:format(cache.resource), function(key, ...)
-	local cb = pendingCallbacks[key]
+    local cb = pendingCallbacks[key]
     pendingCallbacks[key] = nil
 
-	return cb and cb(...)
+    return cb and cb(...)
 end)
 
 ---@param _ any
@@ -16,71 +16,80 @@ end)
 ---@param ... any
 ---@return ...
 local function triggerClientCallback(_, event, playerId, cb, ...)
-	local key
+    assert(DoesPlayerExist(playerId --[[@as string]]), ("target playerId '%s' does not exist"):format(playerId))
 
-	repeat
-		key = ('%s:%s:%s'):format(event, math.random(0, 100000), playerId)
-	until not pendingCallbacks[key]
+    local key
 
-	TriggerClientEvent(cbEvent:format(event), playerId, cache.resource, key, ...)
+    repeat
+        key = ('%s:%s:%s'):format(event, math.random(0, 100000), playerId)
+    until not pendingCallbacks[key]
 
-	---@type promise | false
-	local promise = not cb and promise.new()
+    TriggerClientEvent(cbEvent:format(event), playerId, cache.resource, key, ...)
 
-	pendingCallbacks[key] = function(response, ...)
+    ---@type promise | false
+    local promise = not cb and promise.new()
+
+    pendingCallbacks[key] = function(response, ...)
         response = { response, ... }
 
-		if promise then
-			return promise:resolve(response)
-		end
+        if promise then
+            return promise:resolve(response)
+        end
 
         if cb then
             cb(table.unpack(response))
         end
-	end
+    end
 
-	if promise then
+    if promise then
         SetTimeout(callbackTimeout, function() promise:reject(("callback event '%s' timed out"):format(key)) end)
 
-		return table.unpack(Citizen.Await(promise))
-	end
+        return table.unpack(Citizen.Await(promise))
+    end
 end
 
 ---@overload fun(event: string, playerId: number, cb: function, ...)
 lib.callback = setmetatable({}, {
-	__call = triggerClientCallback
+    __call = function(_, event, playerId, cb, ...)
+        local cbType = type(cb)
+
+        assert(cbType == 'function', ("expected argument 3 to have type 'function' (received %s)"):format(cbType))
+
+        return triggerClientCallback(_, event, playerId, cb, ...)
+    end
 })
 
 ---@param event string
 ---@param playerId number
 --- Sends an event to a client and halts the current thread until a response is returned.
+---@diagnostic disable-next-line: duplicate-set-field
 function lib.callback.await(event, playerId, ...)
-	return triggerClientCallback(nil, event, playerId, false, ...)
+    return triggerClientCallback(nil, event, playerId, false, ...)
 end
 
 local function callbackResponse(success, result, ...)
-	if not success then
-		if result then
-			return print(('^1SCRIPT ERROR: %s^0\n%s'):format(result , Citizen.InvokeNative(`FORMAT_STACK_TRACE` & 0xFFFFFFFF, nil, 0, Citizen.ResultAsString()) or ''))
-		end
+    if not success then
+        if result then
+            return print(('^1SCRIPT ERROR: %s^0\n%s'):format(result,
+                Citizen.InvokeNative(`FORMAT_STACK_TRACE` & 0xFFFFFFFF, nil, 0, Citizen.ResultAsString()) or ''))
+        end
 
-		return false
-	end
+        return false
+    end
 
-	return result, ...
+    return result, ...
 end
 
 local pcall = pcall
 
 ---@param name string
 ---@param cb function
---- Registers an event handler and callback function to respond to client requests.
+---Registers an event handler and callback function to respond to client requests.
+---@diagnostic disable-next-line: duplicate-set-field
 function lib.callback.register(name, cb)
-	RegisterNetEvent(cbEvent:format(name), function(resource, key, ...)
-		TriggerClientEvent(cbEvent:format(resource), source, key, callbackResponse(pcall(cb, source, ...)))
-	end)
+    RegisterNetEvent(cbEvent:format(name), function(resource, key, ...)
+        TriggerClientEvent(cbEvent:format(resource), source, key, callbackResponse(pcall(cb, source, ...)))
+    end)
 end
 
 return lib.callback
-
-