The main reason of this difference it´s because Adinton counts clicks menwhile Google Analytics counts sessions/visits.
Here you will find a link with the definition of «Sessions» by Google.
A Session is a group of interactions that take place on your website within a given time frame.
For this reason, if a user access to your website three times in less than 30 minutes, Adinton is counting 3 clicks and Google Analytics just 1 Session
Normally the ratio (Adinton Clicks)/(GA Sessions) = +/-1.3
NOTE: If Adinton is counting less clicks than Google Analytics visits, it´s because we’ve forgotten to add «utms» labels in some source or we’ve forgotten to add tracker pixel in some pages of our site.
Please visit our post «What’s the difference between Adinton and tools like Google Analytics?» to get more details about de difference between Adinton & Google Analytics.