Recur360 does not have an option to delete a customer once it is created. In QuickBooks you can mark the customer as Inactive.
Then on the next sync with QuickBooks, Recur360 will remove them from the active customer list. You can check the option to Show Inactive Customers at the top of the customer screen if you would like to see the account in Recur360.
Notice if you are using QuickBooks Online the Company Name will show (deleted) in parenthesis behind the name.
If you click on the company you will be able to see the details & history of the customer, but you will not be able to edit the information of process new activity to that customer unless you make them active in QuickBooks again.