The source for a standalone work is usually the publisher or website plus any DOI or URL. If the author is also the publisher, nothing is entered as the publisher. (The location of the publisher is no longer included.) Make sure that the DOI goes to the work itself, not a review about the work. (For more information, see https://apastyle.apa.org/style-grammar-guidelines/references/examples/book-references)

American Psychological Association. (2020). Publication manual of the American Psychological Association (7th ed.). https://doi.org/10.1037/0000165-000 

Barasa, P. L., & Omulando, C. (2018). Research and PhD capacities in Sub-Saharan Africa; Kenya report. British Council and the German Academic Exchange Service. https://www2.daad.de/medien/der-daad/analysen-studien/research_and_phd_capacities_in_sub-saharan_africa_-_kenya_report.pdf 

Blau, P. (2017a). Exchange and power in social life (2nd ed.). Routledge. https://doi.org/10.4324/9780203792643 

Hammond, R. W. (2018). Avoiding the carnage: A guidebook through sales transformation. Informing Science Press.