Q. When should I use a URL for a journal article?

It might help you do understand if you saw a few examples of the different types of URLs.

In this example, the URL has the name of the database in it (Proquest) and you can see that it's trying to search the database for a particular record:

Sweeney, S. (2013). Genrefy your library: Improve readers' advisory and data-driven decision making. Young Adult Library Services, 11(4), 41-45. http://search.proquest.com/docview/1416197427?accountid=16285

Here's another example, this time the database is ScienceDirect:

Yoon, H.-J. (2017). Linguistic complexity in L2 writing revisited: Issues of topic, proficiency, and construct multidimensionality. System, 66, 130-141. https://www.sciencedirect.com/science/article/pii/S0346251X16301348

For this article, from BMJ, the article came from the journal article's site, not a database, so this is the actual URL for the article. See how it starts with the journal, not a database:

Springmann, M., Spajic, L., Clark, M. A., Poore, J., Herforth, A., Webb, P., Rayner, M., & Scarborough, P. (2020). The healthiness and sustainability of national and global food based dietary guidelines: modelling study. BMJ, 370, Article m2322. https://www.bmj.com/content/bmj/370/bmj.m2322.full.pdf

The ScienceDirect article has a DOI, so you can (and should) replace that URL:

Yoon, H.-J. (2017). Linguistic complexity in L2 writing revisited: Issues of topic, proficiency, and construct multidimensionality. System, 66, 130-141 https://doi.org/10.1016/j.system.2017.03.007

The BMJ article also has a DOI, so even though it has a "real" URL for the article, you should still replace it:

Springmann, M., Spajic, L., Clark, M. A., Poore, J., Herforth, A., Webb, P., Rayner, M., & Scarborough, P. (2020). The healthiness and sustainability of national and global food based dietary guidelines: modelling study. BMJ, 370, Article m2322. https://doi.org/10.1136/bmj.m2322

But the Proquest article doesn't, so you would have to see if there's a URL for that article that is on the site for the journal (you may have to Google the article details to find it, as most of our records link to the databases). In this case, there is one: http://www.ala.org/yalsa/sites/ala.org.yalsa/files/content/yalsarchives/Summer2013.vol11.num4.pdf

This URL is a bit long, though. APA 6th used to ask for the URL for the journal itself to get around long URLs like this, but for APA7th you can use a link shortener:

Sweeney, S. (2013). Genrefy your library: Improve readers' advisory and data-driven decision making. Young Adult Library Services, 11(4), 41-45. https://tinyurl.com/y62bqck3

If you couldn't find a stable URL or a DOI to use, you will just finish the reference at the full-stop after the page numbers:

Sweeney, S. (2013). Genrefy your library: Improve readers' advisory and data-driven decision making. Young Adult Library Services, 11(4), 41-45.

N.B. you don't highlight your URLs - they are highlighted in these examples to make it easier to see.