DOI (Digital Object Identifer) provides a persistent electronic link to a journal article or e-book. APA referencing style requires the DOI (where available ) to be included in the Reference List citation.
Example journal article reference with doi:
Braaf, S., Riley, R., & Manias, E. (2015). Failures in communication through documents and documentation across the perioperative pathway. Journal of Clinical Nursing, 24(13/14), 1874- 1884. https://doi:10.1111/jocn.12809.