This email was spam.
It's a vanity press. They're charging you 750 bucks to publish an article. They give you one copy of the book. They are looking for people who are need to list a book chapter in their tenure dossier, and are willing to pay for it. The "royalties" are miniscule compared to your page charges.
I have published some papers with open access models, with page charges from 500-1500, but with legitimate journals boasting a real readership, genuine peer review and listing in major indices along with an impact factor. At my institution, this chapter would make my dossier look weaker, not stronger.
Just a few remarks...
The invitation email isn't spam, only authors selected based on their research history are invited to contribute.
Also, all Sciyo's publications undergo rigorous refereeing. Chapters which don't meet the quality criteria do not get published, meaning it is not vanity publishing or any sort of pay-to-publish scheme. The publishing fee goes towards the actual publishing costs (review and distribution to indices being among them). The information regarding readership can be found at Sciyo's website.