I would assume this falls under Severability [1]. In most cases, the button you click on literally says "I accept", which the corporate lawyer would interpret in a similar way to signing a contract in full.
In other words, if I click "send" on my resignation email to my employer, but later argue in court that I totally didn't mean to actually resign, but only to check if my email program works, I may have a challenging case.
In other words, if I click "send" on my resignation email to my employer, but later argue in court that I totally didn't mean to actually resign, but only to check if my email program works, I may have a challenging case.
[1] https://en.wikipedia.org/wiki/Severability