U don't need ppitch to be a solid professional musician.
True - or U have it or not.
But I knew guys with a ppich who couldn't sing in pitch.
They were really terrible.
But some of them were great musicians.
Don't waste your time and money for this scamy book or what ever it is.
It the same thing if you'll buy a book how to make money with real estate.
What U really need is to learn harmony, scales, theory, and develop a really good relative pitch as mentioned above.
And how to develop this skills is anothers story.
PS A lot of very well known musicians, artists had/have no any idea how to read or write music.
I think It doesn't mean ppl don't have to learn.