Dynamic Value Checkbox Vuejs 2

I can't get the value of the checkbox.

<li v-for="mainCat in mainCategories">
<input type="checkbox" :value="mainCat.merchantId" v-model="mainCategories.merchantId" id="mainCat.merchantId" @click="merchantCategoryId">

</li>

My Methods:

methods: {

            merchantCategoryId: function(){

                console.log(this.mainCategories.merchantId)
            }
        }

When it clicks I only get true and false for uncheck. TY