SUMIF with Date Parameters

Good Afternoon!

I'm looking for a formula that will return the total billings per candidate but only those that fall within certain date parameters.

I have attached a sample workbook for ease of explanation.
Within column D (Current Placements) I need the formula to return the total amount invoiced per candidate but only those with invoice dates that fall within the placement dates.

I have tried a SUMIFS with some greater than and less than but it didn't like that. (I've left my formula in with speech marks so you can see my error).

Any help would be HUGELY appreciated!!
Many thanks,
Laura