Hi Ibrahim,
Have you already compared your code to the Lecture Project Changes which can be found in the Resources of this lecture? And have you already tried to add Debug.Logs to your code to see what is going on during runtime?
If the messages appear, your script gets executed. If the messages do not appear, the code does not get executed. Please figure that out first. Maybe there is a typo in your code, maybe there isn’t.
Secondly, is there an EventSystem in your Hierarchy? If not, add one.
Please let me know if that helped. 
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- Forum User Guides : How to mark a topic as solved