Linking MayFly to existing Arduino IDE heartache

Hello Everyone! I am new to EnviroDIY and am very excited to find this community.
I have recently acquired the MayFly starter kit and intend to deploy and measure ambient temp/humidity as well as use a photosensor to record light levels in the field, save to an SD, as well as posting data onto the internet as some locations have access to WiFi. I have some experience with Arduinos, mostly small projects around the house, I have a bit of background with microprocessors and frankensteining bits of code together.
I am trying to link the MayFly to my Arduino IDE, but I am having some issues.

My IDE version is 1.8.5.
I paste the link provided, https://raw.githubusercontent.com/EnviroDIY/Arduino_boards/master/package_EnviroDIY_index.json, to the “Additional Boards Manager URLs” location.
But when it comes to adding the EnvrioDIY to the board manager, I cannot locate the option of “EnviroDIY ATmega Boards”.
Also, I receive this error in the scratch window of the Arduino IDE:
“no protocol: 1 https://raw.githubusercontent.com/EnviroDIY/Arduino_boards/master/package_EnviroDIY_index.json”

Could it be that the link is no good and it cannot ‘locate’ the EnviroDIY boards?
I did my best to find this material on the forums, but no joy If there is a resource available please point me in the direction!

Thanks everyone!
-Evan