Server Side

When an object is replicated, a request is sent to the server, every time this happens the ReplicationRequest event is fired on the server side, here the server can perform some security checks if you want.

Without security checks

local replicatedStorage = game:GetService("ReplicatedStorage")
local upsideEngineModule = replicatedStorage:WaitForChild("UpsideEngine")

local upsideEngine = require(upsideEngineModule)
local networkingService = upsideEngine.GetService("NetworkingService")

networkingService:On("ReplicationRequest", function(request)
    request:Approve()
end)

With security checks

In this example we check how much the player's character has moved since the last replication, doing this we can detect if the player is using exploits.

local replicatedStorage = game:GetService("ReplicatedStorage")
local players = game:GetService("Players")

local upsideEngineModule = replicatedStorage:WaitForChild("UpsideEngine")
local upsideEngine = require(upsideEngineModule)

local networkingService = upsideEngine.GetService("NetworkingService")
local pastPositions = {}

networkingService:On("ReplicationRequest", function(request)
    local instance = request.Content.Instance
    local clientId = request.ClientId

    if not instance.Position then
        request:Approve()
        return
    end

    local currentPosition = Vector2.new(instance.Position.X.Offset, instance.Position.Y.Offset)
    local previousPosition = pastPositions[clientId] or Vector2.zero

    local distance = (currentPosition - previousPosition).Magnitude
    pastPositions[clientId] = currentPosition

    if distance < 1100 then
        request:Approve()
        return
    end

    -- The player is moving faster than expected, so is probably exploiting
    -- maybe players with lag can have false positives, so be carefull with the distance check

    local player = players:GetPlayerByUserId(clientId)
    player:Kick("please don't exploit")
end)