Unidentified Developer

If you run into this issue, there are three possible ways to get around it.

1. This first method only works on pre-Catalina macOS. If you're on Catalina, skip to the second method.
   Click here for a video tutorial
   Instead of opening the .jar by double clicking, right click the file (ctrl+click) and select Open, like this

The same window will come up, but now there is an Open option next to Cancel, like this:

2. If that doesn't work, open Terminal.app and paste in java -jar ~/Downloads/ImpactInstaller-0.9.5.jar then hit enter.

3. If that doesn't work, open Terminal.app and paste in ~/Library/Application\ Support/minecraft/runtime/jre-x64/jre.bundle/Contents/Home/bin/java -jar ~/Downloads/ImpactInstaller-0.9.5.jar then hit enter. This only works if you already have Minecraft installed and have run it at least once.

4. If that doesn't work, open Terminal.app and paste in JAVA_HOME=~/Library/Application\ Support/minecraft/runtime/jre-x64/jre.bundle/Contents/Home java -jar ~/Downloads/ImpactInstaller-0.9.5.jar then hit enter. This only works if you already have Minecraft installed and have run it at least once.

5. If that doesn't work, open Terminal.app and paste in JAVA_HOME=~/Library/Application\ Support/minecraft/runtime/jre-x64/jre.bundle/Contents/Home ~/Library/Application\ Support/minecraft/runtime/jre-x64/jre.bundle/Contents/Home/bin/java -jar ~/Downloads/ImpactInstaller-0.9.5.jar then hit enter. This only works if you already have Minecraft installed and have run it at least once.

Install a JDK

(Image courtesy of rodridvalle#4072 on the Impact Discord)

If you run into this issue, click on More Info... and follow the instructions on the Java website.