<template lang="pug">
b-modal.simple-modal(
  :active="showUnauthModal"
  width="720"
  scroll= "keep"
  @close="toggleModal"
)
...
 button.is-primary(@click="toggleModal")
 | Go Back
</template>

state: {
    showUnauthModal: false,
  },

toggleModal() {
  this.showUnauthModal = false;
},

watch: {
    something(value) {
      if (value != null) {
        if (value.status === 401) {
          this.showUnauthModal = true; //this is how my modal opens
        }
      }
    },