With vee-validate make custom validation - vuejs2

Question

In my vue 2.5.17 app I have a select input and text input and I have a create a validation rule that only 1 of them musdt be filled :
<div class="form-row p-3">
<label for="existing_user_list_id" class="col-12 col-sm-4 col-form-label">Select already existing list</label>
<div class="col-12 col-sm-8">
<v-select
v-model="selection_existing_user_list_id"
data-vv-name="selection_existing_user_list_id"
:options="userListsByUserIdArray"
v-validate="''"
id="existing_user_list_id"
name="existing_user_list_id"
class="form-control editable_field"
placeholder="Select existing user list"
v-on:input="onChangeSelectionExistingUserListId($event);"
></v-select>
<span v-show="vueErrorsList.has('existing_user_list_id')" class="text-danger">{{ vueErrorsList.first('existing_user_list_id') }}</span>
</div>
</div>
<div class="form-row p-1 m-1 ml-4">
<strong>OR</strong>
</div>
<div class="form-row p-2`">
<label for="new_user_list_title" class="col-12 col-sm-4 col-form-label">Create a new list</label>
<div class="col-12 col-sm-8">
<input class="form-control" value="" id="new_user_list_title" v-model="new_user_list_title" #change="onChangeBewUserListTitle($event);">
<span v-show="vueErrorsList.has('title')" class="text-danger">{{ vueErrorsList.first('title') }}</span>
</div>
</div>
I found this :
https://baianat.github.io/vee-validate/guide/custom-rules.html#creating-a-custom-rule
But I am confused how to use it in my case. I try :
import { Validator } from 'vee-validate';
Validator.extend('new_user_list_title', {
getMessage: field => 'The ' + field + ' value is not a valid new_user_list_title.',
validate: value => false // for simplicity I try to raise error always
// validate: value => value.length == 0 && selection_existing_user_list_id == null
})
But my custom error is never triggered, even when I set always false,
Which is right way ?
Thanks!

Answer 1

After adding custom rule, you need to use it in component (in v-validate):
<input
class="form-control"
id="new_user_list_title"
v-model="new_user_list_title"
#change="onChangeBewUserListTitle($event);"
v-validate="'new_user_list_title'">