In order to delete the recurring invoices, open the Transactions or Expenses -> Recurring page from the Financials menu.
Click on the invoice three-dots menu to open the drop-down and choose "Delete":
Or click on the invoice to view its details and open the Actions menu. Choose the "Delete" option from the drop-down menu:
You will see a pop-up window. Put the checkmark and click Confirm to save changes:
