Spire does not allow a Deposit Sales Order to be deleted because there is a GL Transaction linked to the Sales Order which recorded the deposit.
If the deposit was created in error or the customer canceled the order, perform the following;
1. Add another Deposit with negative amount for the amount of the deposit using the same Payment Method as the original deposit
2. Add a comment on the Sales Order line. For example: "Cancelled deposit"
3. Invoice the Sales Order with a zero Total on the Sales Order
4. Return the deposit amount to the customer if needed
If a refund cheque is required to return the deposit to the customer, then perform the following;