Q. How do I do an APA citation for an Ebrary ebook without a DOI (digital object identifier)?

The APA 7th edition manual states that a citation for an authored e-book without a DOI, if it has a nondatabase URL, should conclude with that URL.

If the e-book is from an academic research database and does not have a DOI, but there is a stable URL (sometimes called a permalink), then your citation should include the URL of the book in the reference. Do not include the name of the database in the citation.

For example, the citation for the e-book The Science of Human Perfection: How Genes Became the Heart of American Medicine, which can be found in the database JSTOR, would look like this: 

Comfort, N. (2012). The Science of Human Perfection: How Genes Became the Heart of American Medicine. Yale University Press. http://www.jstor.org/stable/j.ctt32bqd2 

If the e-book is from an academic research database and there is neither a DOI nor a stable URL, then just end the e-book reference after the publisher name. You should not include the name of the database in the citation. In this case, the citation looks like a reference for a print book.

The source of this answer was from the APA website on their blog: https://apastyle.apa.org/style-grammar-guidelines/references/examples/book-references