It is absolutely inconceivable that as fundamental a function as ENTERING A SALES ORDER is not available to Quickbooks Online Users.  WTF!!!???  An estimate is not the same thing as a sales order.  When you receive a purchase order, you don't respond by giving the customer an ESTIMATE.  Nor do you give them an INVOICE.  The sales order is the step in between the estimate and the invoice, like you car is in between your home and your office.  FIGURE THIS OUT.  I am embarrassed for you, and for myself for paying for this garbage.