hello, I am using the C# SDK, is there any difference on usage if I'm using this SDK? Does it mean that this SDK can only be use on my backend (Code base) or I can also use this for client side(front-end)?

what is your front-end built in? it has a dependency on .NET which is supported in windows desktop app development, but if you're asking about web, you'll need to use the javascript SDK (or react).