They are two different things.
iPromote reports every click. From an iPromote perspective, there is a one-to-one correlation between a click and navigation to the landing page.
However, Google Analytics reports sessions. A session involves several steps after a click and is not restricted to a single event. It is rather a meaningful set of "interactions" that occur within a specific timeframe on a given website. Google documentation states that "[y]ou can think of a session as the container for the actions a user takes on your site."
There's no fix for the problem. Knowing the difference between clicks and sessions is important because they are two very different things.
For more information, see The difference between Google Ads Clicks, and Sessions, Users, Entrances, Pageviews, and Unique Pageviews in Analytics.