Why is validation not working properly?

Hello everyone, I am experiencing an issue with form validation after submission. I attempted to create two reservations simultaneously in separate browsers. Although they were not created at exactly the same time, I have configured the system such that a reservation can only have one unique available business hour ID. However, I am still able to create two reservations for the same unique available business hour ID at the same time. I cannot figure out why this is happening.

this is my component

<?php

namespace App\Livewire;

use Livewire\Component;
use App\Models\Reservation;
use App\Mail\ReservationMail;
use Illuminate\Support\Facades\Mail;
use App\Models\AvailableBusinessHour;

class Booking extends Component
{
    public $full_name;
    public $email;
    public $phone_number;
    public $reservation;

    public $selectedService;
    public $available_business_hour_id;
    public $selectedBusinessHourId;
    public $verification_code;
    public $successMessage;
    public $successMessageVisible;
    public $successMessageTimeout = 3000;
    public $verificationCodeSubmitted = false;
    public $successMessageClosed = false;


    public function getAvailableBusinessHours()
    {
        return AvailableBusinessHour::whereDoesntHave('reservation')
            ->where(function ($query) {
                $query->where('day', '>', now()->format('Y-m-d'))
                    ->orWhere(function ($query) {
                        $query->where('day', '=', now()->format('Y-m-d'))
                            ->where('from', '>', now()->format('H:i'));
                    });
            })
            ->orderBy('day')
            ->orderBy('from')
            ->get();
    }



    public function render()
    {
        $this->available_business_hour_id = $this->getAvailableBusinessHours();
        return view('livewire.booking', [
            'emptyOption' => 'Vyber si čas rezervace',
        ]);
    }

    public function store()
    {
        $this->validate([
            'full_name' => 'required|string|max:250',
            'email' => 'required|email|max:250',
            'phone_number' => 'required|phone:CZ',
            'selectedService' => 'required',
            'available_business_hour_id' => 'required|unique:reservations'
        ], [
            'available_business_hour_id.unique' => 'Tento termín byl již obsazen, vyber jiný pokud je nějaký dostupný.',
            'available_business_hour_id.required' => 'Výběr času objednání je povinné pole.',
            'phone_number.phone' => 'Chybný formát telefonního čísla.',
            'selectedService.required' => 'Toto je povinné pole',
        ]);

        $selectedBusinessHour = AvailableBusinessHour::find($this->selectedBusinessHourId);


        if (
            $selectedBusinessHour->day < now()->format('Y-m-d') ||
            ($selectedBusinessHour->day == now()->format('Y-m-d') && $selectedBusinessHour->from < now()->format('H:i'))
        ) {
            $this->addError('selectedBusinessHourId', 'Tento termín již není dostupný, vyber jiný.');
            return;
        }

        $verification_code = rand(100000, 999999);

        $reservation = Reservation::create([
            'full_name' => $this->full_name,
            'email' => $this->email,
            'phone_number' => $this->phone_number,
            'service' => $this->selectedService,
            'available_business_hour_id' => $this->selectedBusinessHourId,
            'day' => $selectedBusinessHour['day'],
            'from' => $selectedBusinessHour['from'],
            'to' => $selectedBusinessHour['to'],
            'verification_code' => $verification_code
        ]);
        dd($reservation);

        session(['verification_code' => $verification_code, 'current_reservation_id' => $reservation->id]);


        $this->sendReservationConfirmationMail($reservation);


        $this->dispatch('show-verification-modal');
        $this->dispatch('update-success-message', ['closed' => $this->successMessageClosed]);


        $this->reset(['full_name', 'email', 'phone_number', 'available_business_hour_id']);
    }

    public function sendReservationConfirmationMail($reservation)
    {
        Mail::to($reservation->email)->send(new ReservationMail($reservation));
    }

    public function services()
    {
        return ["Stříhání vlasů", "Stříhání + úprava vousů", "Barvení vousů", "Junior střih", "Úprava vousů"];
    }

    public function confirmReservation()
    {
        $this->validate([
            'verification_code' => 'required|digits:6',
        ], [
            'verification_code.required' => 'Zadejte prosím verifikační kód.',
            'verification_code.digits' => 'Verifikační kód musí mít 6 čísel.',
        ]);

        $user_entered_code = $this->verification_code;

        $reservation = Reservation::where('verification_code', $user_entered_code)
            ->where('is_confirmed', false)
            ->where('id', session('current_reservation_id'))
            ->latest()
            ->first();

        if ($reservation) {
            $reservation->update(['is_confirmed' => true]);
            $this->reset(['verification_code']);
            $this->successMessage = 'Rezervace proběhla úspěšně.';
            $this->successMessageVisible = true;
            $this->dispatch('hide-verification-modal');
            $this->dispatch('update-success-message', ['closed' => $this->successMessageClosed]);
        } else {
            $this->addError('verification_code', 'Neplatný verifikační kód nebo rezervace již byla potvrzena.');
        }
    }
}

this is blade

    <div class="container">
        @if ($successMessageVisible && !$verificationCodeSubmitted)
            <div x-data="{ show: @entangle('successMessageVisible'), closed: @entangle('successMessageClosed') }" x-init="setTimeout(() => { show = false; if (!closed) Livewire.emit('refresh-view'); }, {{ $successMessageTimeout }})" x-show="show" class="alert alert-success text-center">
                {{ $successMessage }}
            </div>
        @endif
        <form wire:submit.prevent="store">
            @csrf
            <div class="col-12 mb-4">
                <h1 class="modal-title fs-5 text-center" id="bookingModalLabel">Objednej se</h1>
                <p class="text-center">Lorem, ipsum dolor sit amet consectetur adipisicing elit. Lorem, ipsum
                    dolor sit amet consectetur adipisicing elit.</p>
            </div>
            <div class="form-group col-12">
                <input type="text" wire:model="full_name" id="full_name" name="full_name" class="form-control"
                    placeholder="Celé jméno*" required>
            </div>
            <div class="form-group col-12">
                <input type="email" wire:model="email" id="email" name="email" class="form-control"
                    placeholder="Email*" required>
            </div>
            <div class="form-group col-12">
                <input type="text" wire:model="phone_number" id="phone_number" name="phone_number"
                    class="form-control" placeholder="Tel. číslo ve formátu +420700700700" required>

                @error('phone_number')
                    <span class="text-danger">{{ $message }}</span>
                @enderror
            </div>
            <div class="form-group col-12">
                <select wire:model="selectedService" class="form-control">
                    <option value="">Vyberte službu</option>
                    @foreach ($this->services() as $service)
                        <option value="{{ $service }}">{{ $service }}</option>
                    @endforeach
                </select>
                @error('selectedService')
                    <span class="text-danger">{{ $message }}</span>
                @enderror
            </div>

            <div class="form-group col-12 mt-3">
                <select wire:model="selectedBusinessHourId" class="form-control">
                    <option value="">{{ $emptyOption }}</option>
                    @foreach ($available_business_hour_id as $time)
                        <option value="{{ $time['id'] }}">{{ $time['formattedDayAndDate'] }} od {{ $time['from'] }} do
                            {{ $time['to'] }}</option>
                    @endforeach
                </select>
                @if ($errors->has('available_business_hour_id') && !$errors->has('selectedBusinessHourId'))
                <span class="text-danger">{{ $errors->first('available_business_hour_id') }}</span>
            @endif
            @if ($errors->has('selectedBusinessHourId'))
                <span class="text-danger">{{ $errors->first('selectedBusinessHourId') }}</span>
            @endif
            </div>
            <div class="form-group col-12 text-center">
                <div class="cta-btns">
                    <button type="submit" class="btn btn-service me-sm-2">Odeslat</button>
                </div>
            </div>
        </form>

    </div>

I will be glad for any advice.