This article will explain how to activate 'Hybrid Mode' on your Dynamic Search Campaign.
Not sure what Hybrid Mode is? Check out the following article for more details: What is Hybrid Mode?
Make sure you are under the Campaigns tab, and under the 'Dynamic Search Campaigns' Creation menu option
Select the relevant campaign and open the sync settings icon ()
Change the 'Sync Keywords' as well as the 'Sync Ads' option to 'Add Only'.