Registration: "Something went wrong. Please try again or contact customer support."

I have followed this documentation: https://spark.laravel.com/docs/3.0/adding-registration-fields

Here's my code:

register-common-form.blade.php:

    <!-- Timezone -->
    <?php require(app_path().'/Includes/timezones.php'); ?>
    <div class="form-group" :class="{'has-error': registerForm.errors.has('timezone')}">
        <label class="col-md-4 control-label">Timezone</label>

        <div class="col-md-6">
            <select class="form-control" name="timezone" v-model="registerForm.timezone">
            @foreach ($timezones as $formTimezone => $utc)
                <option value="{{ $formTimezone }}">{{ $utc }}</option>
            @endforeach
            </select>

            <span class="help-block" v-show="registerForm.errors.has('timezone')">
                @{{ registerForm.errors.get('timezone') }}
            </span>
        </div>
    </div>

app.js

/*
 |--------------------------------------------------------------------------
 | Laravel Spark Bootstrap
 |--------------------------------------------------------------------------
 |
 | First, we will load all of the "core" dependencies for Spark which are
 | libraries such as Vue and jQuery. This also loads the Spark helpers
 | for things such as HTTP calls, forms, and form validation errors.
 |
 | Next, we'll create the root Vue application for Spark. This will start
 | the entire application and attach it to the DOM. Of course, you may
 | customize this script as you desire and load your own components.
 |
 */

require('spark-bootstrap');

require('./components/bootstrap');

Spark.forms.register = {
    timezone: ''
};

var app = new Vue({
    mixins: [require('spark')]
});

SparkServiceProvider.php

<?php

namespace App\Providers;

use Laravel\Spark\Spark;
use Laravel\Spark\Providers\AppServiceProvider as ServiceProvider;

class SparkServiceProvider extends ServiceProvider
{
    /**
     * Your application and company details.
     *
     * @var array
     */
    protected $details = [
        'vendor' => 'Your Company',
        'product' => 'Your Product',
        'street' => 'PO Box 111',
        'location' => 'Your Town, NY 12345',
        'phone' => '555-555-5555',
    ];

    /**
     * The address where customer support e-mails should be sent.
     *
     * @var string
     */
    protected $sendSupportEmailsTo = null;

    /**
     * All of the application developer e-mail addresses.
     *
     * @var array
     */
    protected $developers = [
        //
    ];

    /**
     * Indicates if the application will expose an API.
     *
     * @var bool
     */
    protected $usesApi = true;

    /**
     * Finish configuring Spark for the application.
     *
     * @return void
     */
    public function booted()
    {
        Spark::useStripe()->noCardUpFront()->trialDays(10);

        Spark::freePlan()
            ->features([
                'First', 'Second', 'Third'
            ]);

        Spark::plan('Basic', 'myapp-test-1')
            ->price(10)
            ->features([
                'First', 'Second', 'Third'
            ]);

        Spark::validateUsersWith(function () {
            return [
                'name' => 'required|max:255',
                'email' => 'required|email|max:255|unique:users',
                'timezone' => 'required|max:50',
                'password' => 'required|confirmed|min:6',
                'vat_id' => 'max:50|vat_id',
                'terms' => 'required|accepted',
            ];
        });

        Spark::createUsersWith(function ($request) {
          $user = Spark::user();
          $data = $request->all();
          $user->forceFill([
              'name' => $data['name'],
              'email' => $data['email'],
              'timezone' => $data['timezone'],
              'password' => bcrypt($data['password']),
              'last_read_announcements_at' => Carbon::now(),
              'trial_ends_at' => Carbon::now()->addDays(Spark::trialDays()),
          ])->save();
          return $user;
        });
    }
}

I have added

$table->string('timezone')->nullable();

to my create_users_table migration

I have updated my Users.php model to add timezone:

    protected $fillable = [
        'name',
        'email',
        'timezone',
    ];

When I attempt to register a new user with my app, I get the following error: "Something went wrong. Please try again or contact customer support."

What did I miss?