I would place the distinction on how much of your focus is required to make the micropayment or to oversee it.

Sure, I pay a price in energy to walk somewhere or to lift something, but for me, the relevant question is not the cost so much as the cost of my being aware of it.

Let's imagine renting a movie from Amazon or YouTube. This comes with a dollar price tag as well as a mental price tag in deciding to rent the movie. A typical movie might be a couple hours of entertainment. Spending a few seconds deciding to psy the rental price doesn't seem unduly burdensome.

Reading an article maybe takes ten minutes. It still might make sense to spend the attention necessary to decide if I want to pay for it or not. Although I could see it becoming annoying if you were researching some topic and browsing through a lot of articles.

Paying to read a note on nostr or x (no matter how small the price) might be truly frustrating. If you paid for every note the app loaded you might be really frustrated if there was lots you weren't interested in. Or you might discover that the app had recently changed its pricing and you might end up spending more then you intended.

The idea is that whatever the monetary cost of an action actually is, it carries an extra price in terms of your attention required to decide whether the price is worth paying.