If the entity was created client side then you **can ** remove it using any removal method that you want. The reason why you are getting that error is because you’re trying to remove an entity from the server realm. This goes the same for server trying to remove clientside entities (well the server wouldn’t actually know they exist since they are on the client)
In order to remove an entity from the server requested from the client realm, you would basically have to tell the server to remove that entity through any kind of networking operation such as the net library.
SafeRemoveEntity is the same as entity:Remove() except it has some extra checks that you don’t have to write such as making sure the entity you’re trying to remove is valid and that the entity you’re trying to remove is not a player