The doi is preferred over the URL.
Format it as
Author, A. (2010). How to find a doi number. The Journal of Citing Sources, 8(1). 38-48. https://doi.org/10.21061/jots.v39i1.a.1
To locate the DOI
If you tried Steps 1-3, give up on the doi. Not every article has one.
Instead, paste the journal's home page URL (web address) into the reference entry. Don't use the page where the article is actually located, always use the home page.
Author, A. (2010). How to find a doi number. The Journal of Citing Sources, 8(1). 38-48. Retrieved from http://www.ThisIsTheJournalWebsite.com
Thus saith APA.
Citing an UpToDate topic:
Cite the UpToDate topic as a chapter in an electronic book titled UpToDate, edited by Denise S. Basow. There are no page numbers to cite, and the publication year for any topic should be the current year.
Marion, D.W. (2013). Diaphragmatic pacing. In D. S. Basow, (Ed.), UpToDate. Retrieved from http://www.uptodate.com/home