The Fixed Price Options selection criteria can be used to indicate which optional values will be generated by the post:
Post Billable Fixed Price -- When checked, Fixed Price billable items will be generated by the post. This should be checked if you want to create new FP items to appear on invoices.
Post Fixed Price Revenue -- When checked, Fixed Price revenue will be posted. This should be unchecked if you only want to create new billable transactions for your FP projects. Note that this does not affect revenue recognition for FP items where revenue is recognized when billed.