Adjust total price in commerce checkout

I have a store setup with 2 products. Public and private tours. Public tours are 10 for each unit.

Private tours on the other hand are only meant to collect a deposit. I need the total to be $50 no matter the quantity selected and the rest is paid on site.

I tried creating a custom PromotionOffer as seen below. I can create the promotion but it doesn't seem to apply while in the cart/checkout. I even tried making it a coupon and when I apply the coupon it says its not valid, may have expired or been used. I have one condition set and that is they have a private tour in their cart.

<?php

namespace Drupal\tour_reservation\Plugin\Commerce\PromotionOffer;

use Drupal\commerce_order\Adjustment;
use Drupal\commerce_price\Price;
use Drupal\commerce_promotion\Entity\PromotionInterface;
use Drupal\commerce_promotion\Plugin\Commerce\PromotionOffer\PromotionOfferBase;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Form\FormStateInterface;

/**
 * Discounts a cart to a fixed amount.
 *
 * @CommercePromotionOffer(
 *   id = "tour_reservation_discount_to_fixed",
 *   label = @Translation("Sets cart total to a fixed amount"),
 *   entity_type = "commerce_order_item",
 * )
 */
class OrderFixedPrice extends PromotionOfferBase {

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'amount' => NULL,
    ] + parent::defaultConfiguration();
  }

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $form += parent::buildConfigurationForm($form, $form_state);

    $amount = $this->configuration['amount'];
    // A bug in the plugin_select form element causes $amount to be incomplete.
    if (isset($amount) && !isset($amount['number'], $amount['currency_code'])) {
      $amount = NULL;
    }

    $form['amount'] = [
      '#type' => 'commerce_price',
      '#title' => $this->t('Amount'),
      '#default_value' => $amount,
      '#required' => TRUE,
      '#description' => $this->t('Set cart price. Format: 9.99'),
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
    $values = $form_state->getValue($form['#parents']);
    if ($values['amount']['number'] < 0) {
      $form_state->setError($form, $this->t('Amount cannot be negative.'));
    }
  }

  /**
   * {@inheritdoc}
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
    parent::submitConfigurationForm($form, $form_state);

    $values = $form_state->getValue($form['#parents']);
    $this->configuration['amount'] = $values['amount'];
  }

  /**
   * {@inheritdoc}
   */
  public function apply(EntityInterface $entity, PromotionInterface $promotion) {
    $this->assertEntity($entity);
    /** @var \Drupal\commerce_order\Entity\OrderItemInterface $order_item */
    $order_item = $entity;
    $target_amount = $this->getAmount();
    $order_item->addAdjustment(new Adjustment([
      'type' => 'promotion',
      'label' => t('Discount'),
      'amount' => $target_amount,
      'source_id' => $promotion->id(),
    ]));
  }

  /**
   * Gets the offer amount.
   *
   * @return \Drupal\commerce_price\Price|null
   *   The amount, or NULL if unknown.
   */
  protected function getAmount() {
    if (!empty($this->configuration['amount'])) {
      $amount = $this->configuration['amount'];
      return new Price($amount['number'], $amount['currency_code']);
    }
  }

}

Ideally, I dont want to use promotions and rather just adjust the price in the cart. Any ideas?