App Store > macOS High Sierra > Download
We could not complete your purchase.
You do not have enough space to install macOS High Sierra.
[ Learn More ] [ OK ]
That [ Learn More ] button does nothing at all. I opened the Console app and filtered the messages using "App Store" and I found this:
Rejected request to open untrusted URL DABuyButtonLearnMoreURL.Yosemite
I'm running macOS Sierra 10.12.6
Best Answer
I had the same issue and I thought I had enough space but I didn't. You need at least 14.3GB I believe. It downloaded for me afterwards