Q. Should I include a URL in my APA citation? If so, what URL?
APA prefers that you use a DOI rather than a URL. If a DOI is present, it should be included, even for sources where you are using a physical copy. The DOI should be expressed using the syntax
https://doi.org/. Optionally, you may shorten the DOI using shortDOI.
In the case of an online resource that has no DOI, you may need to include a URL.
If the source is from a non-database website, include the URL. Do not use the words "Retrieved from" as was recommended in earlier editions of the APA Manual. These works can be treated as if you were using them in print.
If the source is in an academic research database, no URL is necessary, even if there is no DOI. The exception is the case of a database that publishes unique information, such as ERIC. In this case, the database should be mentioned (as it is the source, not just the purveyor, of the publication) and a URL provided.
Yes, it’s all a bit complicated. For more detail, see section 9.34 of the Manual (7th ed.).