How to turn two input fields into a key/value pair?

I have a custom child component with 2 inputs. The first input is for the Expense value which I want to be the key and the second input is for the “Expense” Amount value.

Ex: {Expense: Amount} or {Shopping: 200}

Child Component

<input type="text" placeholder="Expense" :value="expenseKey 
@input="$emit('expenseKey', $event.target.value)" />

<input type="number"  placeholder="Amount" @input="$emit('input', { 
        value: $event.target.value,
        id
      })"/>

<script>
export default {
  name: "formInput",
  props: {
    id: Number,
    expenseKey: Array
  }
};

In the parent component I want to submit both inputs values as key/pairs via POST request to my Express Api.

Parent Component
Note: I admittedly added code that I felt was relevant if you would like to see the whole parent component, let me know!

<template>

<form-input v-for="(n,idx) in count"  :key="n" :id="idx"
      :expenseKey="expensesKey" @expenseKey="expensesKey = $event"
      @input="getExpense">
      </form-input>

<button type="button" @click="submitBudget">Submt</button>


  <p>Expense: {{ expensesKey }}</p>
  <p>Amount: {{ expenses }}</p>

</template>
<script>

import axios from "axios";
import formInput from "../components/Input.vue";

export default {
  components: {
    "form-input": formInput
  },
  name: "form",
  data() {
    return {
      count: 0,
      earnings: "",
      expenses: [],
      expensesKey: [],
      totalExpense: ""
    };
  },
submitBudget() {
      axios
        .post("http://localhost:3000/budget", {
          earning: this.earnings,
          expenseValue: this.expenses,
          expenseKey: this.expensesKey
        })
        .then(response => {
          console.log(response.data);
        })
        .catch(e => {
          console.error(e);
        });

let obj={}
obj[Expense]=Amount