Hey @YiannisSk !
Unfortunately, adding a coupon code directly into an email isn't possible because it relies on Javascript, which emails can't use.
Here's a quick approach on how did I achieve this :
We can create a unique URL for each member using their coupon code. This way, when they click the link in the email, it automatically adds the code for them.
For example, your string would look like this when you code it: href="http://www.yousite.com/?[%coupon%]," and your ESP will do the rest, provided the database is set up correctly.
Hope this helps!
Regards,
Abhinav