Finding your Skype ID is very easy, and it takes 30 seconds.

Log into your Skype account, click on your Skype picture and then on the "Skype profile" button. A new window will pop up.
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Scroll down a little, and you will see your Skype ID at "Skype Name"

Your Skype ID can have one of the two formats:

Either way, your Skype ID will be valid. Make sure to correctly copy it!