If you are an existing user in Celoxis and decided to switch to QBO you need to first agree on date prior to making the switch. This is important because once you are connected to QBO you can only sync the time entries which in Approved and Billable state. You cannot sync entries which are already in Invoice state hence if you want to sync entries in Invoiced state you need first UnInvoice them (This action can be performed only by privileged user) and then sync with QBO. There will be no Invoice button in bulk operations or single edit for Approved TE.