Why does Chrome keep displaying “Site cannot be installed: the page is not served from a secure origin” in the console?

Question

Whenever I look in Chrome\'s console, I see this error message:

Site cannot be installed: the page is not served from a secure origin

Answer 1

In later versions of Chrome, this can occur as a result of a flag relating to banner content serving. These flags change all the time, but here's how it looks in Chrome 78:

The flag is bypass-app-banner-engagement-checks, and it's pretty far down the screen (unless it's enabled, in which case it's near the top of the screen).

Answer 2

2019-Dec update: this answer is outdated. Neither of the two flags mentioned in it are available in Chrome any more. Old answer below.

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This error is caused by sites served over HTTP if "Add to shelf" is enabled in chrome://flags.

Solution: go to chrome://flags/#enable-app-banners (used to be chrome://flags/#enable-add-to-shelf) and change "Enabled" to "Default", then relaunch Chrome.