The app has not been integrated on the theme you check

You can check issue as follows:

1. From the app admin page, click Settings
2. On the Settings page, select Themes
3. Select the theme you want to check > click Integrate
4. Go back to Shopify admin page, click Online stores
5. Click Themes > preview the theme you’ve integrated in step 3 to check the result

The booking-set product has not been available

You can check this issue as follow

1. From Shopify admin page, click Products folder
2. From the product list, click on the product you want to check
3. In Product availability section, check if it is available
4. If it is not, click Manage button
5. A popup will show up, tick to make it available on Online store
6. Click Save