Click a button inside an iframe

The Practice Hub component lab embeds a policy frame:

html

<iframe title="Practice content frame" name="practice-frame"
        srcdoc="<main><h1>Iframe checkout policy</h1><button id='frame-action'>Acknowledge</button></main>">
</iframe>

A test needs to click #frame-action and then assert on a message that appears in the parent page afterwards.

The current attempt throws NoSuchElementException:

java

driver.findElement(By.id("frame-action")).click();

Your task: explain the failure, write a correct version in Selenium and Playwright, and identify the mistake that will break the parent-page assertion even after the click starts working.