An exchange that is so valuable, where your e-book is so valuable that you could easily sell it for 20-30 €.
But you give it away for free in quotation marks in exchange for the email.
I know there are rules with GDPR and so on.
You just have to make it clear that people are subscribing to the newsletter and so on, no linking allowed.
“Hey, enter your czech republic telegram screening email here to get the book”
and suddenly they're constantly getting newsletters from you.
Instead, you have to make it clear that they are subscribing to a newsletter and, as a gift, they will receive this e-book.
This has to be clear so that it is understandable from a data protection perspective.
So that people know that they are really subscribing to a newsletter.
But once you have communicated this clearly and well and presented the book in a very seductive way, you again need good copywriting.