It's not that... but rather... / It's not... it's...
Used to correct a misunderstanding by replacing what isn't true with what is. No es que + subjunctive, sino que + indicative.
It's not that I don't want to help, but rather I don't have time.
It's not that it's difficult, it's that it requires practice.
—Don't you like it? —It's not that I don't like it, but rather it's not for me.