Troubleshooting

The customer does not see the waiting box

The order is not Processing. Only Processing orders, and On hold orders paid with a manual method you selected, wait for confirmation. See Which orders can be confirmed.
WooCommerce does not show the order details. The page shows the status only to the person who placed the order: guests directly after checkout (later after confirming their email address), registered customers when logged in. See Who can see the status.
A page cache serves an old page. Exclude the checkout and order received pages from page caching (most cache plugins do this for WooCommerce pages automatically).

The page checks every 5 seconds until Time before timeout. After that, the customer is asked to check their email. Raise the timeout under Advanced if you often answer later.
A security or cache plugin that blocks admin-ajax.php for visitors stops the updates.

The confirmation form is read-only for orders that are not Processing (or a selected manual On hold method), for example orders that are already confirmed, completed or cancelled.
With Order Fulfillment Time on, the preview asks for a time in the future.

Click the bell button; the sound is off when the page opens.
Click Continue when the page shows Order bell is activated; browsers block sound until you click on the page.
Check the volume of the device and that the browser tab is not muted.
With Alert only processing orders? on, unpaid Pending payment orders do not ring.

Cancelled Order to Customer is sent only when you reject an order with Reject (from version 1.1.8). Before 1.1.8 it was sent for every cancelled order while Ability to deny order? was on.
WooCommerce’s own Processing order email is still sent unless you turn it off.

The store may be closed with the Open / Close switch on the Live Order Page. Open it with the same switch.

Use Contact & support. Tell us the WooCommerce version, whether you use the Checkout block or the classic checkout, and the order status.