The DOI or URL is the final component of a reference list entry. Because so much scholarship is available and/or retrieved online, most reference list entries end with either a DOI or a URL.
Follow these guidelines to format DOIs and URLs:
https://doi.org/xxxxx
The location of the DOI can depend on many things. Here are some places to look for the DOI:
Not every electronic journal article has a DOI. If no DOI is available and you retrieved the journal article online, you should include the persistent URL.
DOIs and URLs are covered in Sections 9.34 to 9.36 of the APA Publication Manual, Seventh Edition