I have followed every line in order and am able to setup all other kinds of server. I got this server pack from forge and this is what I get every time. Thanks in advance!

Starting SevTech Ages of the Sky Server...
A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
at net.minecraft.launchwrapper.Launch.(Launch.java:34)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
... 6 more
Press any key to continue . . .

@TrevorB13: hello! 👋

This issue is being automatically closed because it does not follow the issue template.

You must use Java 8. Forge for 1.12.2 is incompatible with later versions of Java.

If you need further help, please use the Discord server - https://discord.gg/darkosto