{
"payments" : {
    "paymentId" : {
        "amount" : "12",
        "toId" : "userId2",
        "fromId" : "userId1",
        "for" : "lunch"
    }
},

"users" : {
    "userId1" : {
        "name" : "Alex",
        "email" : "alex@gmail.com"
    },
    "userId2" : {
        "name" : "Ben",
        "email" : "ben@gmail.com"
    },
    "userId3" : {
        "name" : "Charles",
        "email" : "charles@gmail.com"
    }
}