What is the easiest/fastest way to implement Unity multiplayer?

The implementation of multiplayer is naturally possible in Unity. Nevertheless, Unity is a game engine in which real programming takes place. According to this, Unity cannot simply deploy servers and say, “Here, please.” First and foremost, it is recommended to have a server. Of course, it costs money. How much performance this needs depends on your program. I don’t know if Unity already delivers or not. But there are many providers. It is important here that you look at performance and price, as well as service, and do not dare to pay attention to unity. It can always be that another provider that is not specifically for Unity is cheaper. It won’t be easy. As already said, Unity can’t just deliver anything and it’s okay. They don’t know your code. Some APIs may be available, but I can imagine less. You need to think about how you want to implement it. HTTP is probably the wrong protocol. You can watch TCP/UDP. Make sure what specialties they have and when to use them. There are also protocols that build on such as WebSockets, SignalR, etc. You can look around. These protocols allow you to communicate virtually live with the server. Then you have to decide what it’s going to be. I currently work with console applications for my servers. It is simply a personal preference, as it is simple and fast. Then you have to deal with the fact that many data have to be checked so that no one manipulates them. SSL may also be a topic and encryption. Databases where you store the data are also important. I’m a fan of MySQL. But what makes sense for you will have to analyze. Precisely code, which occurs twice as testing data, can be stored in DLLs, so that you only have to write it once and can apply it for server and client. Generally, however, this is only Grobe information to give you an idea. You can do further research with them.