They’re part of the reason it’s not free any more.

Well, Salesforce could have made the free dynos non-commercial only

That's even worse, so when your hobbyist project accidentally makes 40$ Salesforce can send it's legal team after you?

I would prevent any hobbyist project of mine from making $40 for tax reasons alone, where the difference the to tax authorities between $0 and $40 is basically the same as the difference to a Saleforce non-commercial clause. At $0 I don’t have to do anything about taxes. At $40 it’s immediately in the red due to whatever time I have to spend sorting out taxes for $40 in revenue.

I'm not an accountant, but for the US in 2021, that was Form 1040, Schedule 1: Additional Income and Adjustments to Income, Part 1: Additional Income, line 8: Other income, sub-line i: Activity not engaged in for profit income. You would just put $40 on that sub-line and add it to your adjusted gross income. If you made only $40 on it, I don't it can reasonably be called self-employment income, per Publication 535.

[0] https://www.irs.gov/instructions/i1040gi#en_US_2021_publink1...

[1] https://www.irs.gov/pub/irs-pdf/p535.pdf

Right, and I'm not in the US, but my point is that even if it is that simple, figuring that out for my country and filling out the form is going to take more than $40 worth of my time, and introduces downside risk that I've gotten it wrong somehow.