Useful information to include:

• Minecraft version 1.15.2
• CC: Tweaked version 1.15.2-1.88.1
• Detailed reproduction steps: sometimes I can spot a bug pretty easily, but often it's much more obscure. The more information I have to help reproduce it, the quicker it'll get fixed.

I'm trying to get my kid into programming through ComputerCraft. There is a book with a companion website: https://turtleappstore.com/help/#installing_the_appstore_app that provides some guidance on this. We were using 1.8.9 because that was the latest that the old ComputerCraft supports, but I found this awesome mod, so I've been trying to put it to work, but found that the turtle App Store which is how I had been loading my code on before doesn't work. Looking Into it, it appears that the http.get call is the culprit, and while http.get("https://google.com") properly returns something, lots of other legit urls including https://turtleappstore.com don't. the request returns nil, so I haven't been able to debug what might be going wrong. How can I help get this fixed?

I figured out a little bit more, and can see that turtleappstore.com and some other working sites I tested return "Could not connect" It isn't much, but more than I had before.

Older versions of Java, including the one the vanilla launcher uses, do not bundle the LetsEncrypt certificates, which means they cannot securely connect to the server.

Updating to Java 8u101 or above should fix this (if you're using the vanilla launcher, I'm afraid you'll need to change it to use a custom Java version).

Excellent info, thanks!

Just for anyone else who's GoogleFu brings them to this page, here were the steps to fix it for me on the Mac.

Install a newer version of Java.

Launch the Minecraft vanilla launcher
Click installations and edit the one I'm trying to adjust
Select More Options
Click Browse next to Java Executable
In my case I selected /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/bin/java
Click Save and Play as normal.