Can't install ESP32

I'm trying to install the ESP32 stuff. I have the correct URL in “Additional Board Manager URLs”, but I'm getting an error:

Error downloading https://dl.espressif.com/dl/package_esp32_index.json

I can put the URL into a browser and get the JSON, though. Is there a minimum version of the Arduino IDE required? I'm at 1.6.11. I have the ESP8266 stuff installed without a problem.

I found a github URL that allowed me to proceed, but the install still failed. So I’m thinking it must be the IDE version. I have IDE 1.8 on a different machine and it worked fine.