A digital object identifier (DOI) is a series of numbers and characters assigned permanently to any entity - for instance, a journal article - for use on digital networks, and it generally appears somewhere toward the end of an item record in a database. The DOI is used to provide current information about an item, including where the item (or information about it) can be found on the Internet. Here is an example of a DOI:
https://doi.org/10.1177/0145445512445609
To find a DOI for an item, you can copy and paste the article title into the search box at https://search.crossref.org/
DOIs may be either underlined or not but should be live links if the work is to be published or read online.
NOTE: Include a DOI for all works that have a DOI, regardless of whether you used the online version or the print version.
When adding the DOI to a reference, APA requires you include the prefix https://doi.org/ followed by the DOI (starting with 10. and everything that follows). You may have to change the format of DOIs you retrieve in your research to comply with APA's rules. (APA 7, 9.35 ). See the example below:
Dills, A. K., Morgan, H. N., & Rotthoff, K. W. (2011). Recess, physical education,
and elementary school student outcomes. Economics of Education Review, 30(5),
889-900. https://doi.org/10.1016/j.econedurev.2011.04.011