A booking can not be deleted if there is an invoice or any payment attached to it. So you would first need to delete the invoice/payments from the booking (if using an accounting integration, please note if you delete the invoice/invoice, it will also be deleted from Xero/Quickbooks).

In most cases, it is better to simply mark the booking as Canceled or Lost. If you have received any payments on a booking, even if the booking is canceled it is best to keep a record of the payment. You should maybe change your products to "Retained Deposit" for an amount equal to the invoice/payment amount, so the products and invoice/payments will equal each other.