1.12 FMLLaunchHandler.isDeobfuscatedEnvironment()Z

Hello, I don't know anything about coding, and while installing a pack of mods on minecraft 1.12, I've had this error come up. Would anybody know what to do? While installing the same mods into a technic launcher 1.12 modpack, everything worked fine.

Thank you for your help!

Time: 4/24/20 5:05 PM
Description: Initializing game

java.lang.NoSuchMethodError: net.minecraftforge.fml.relauncher.FMLLaunchHandler.isDeobfuscatedEnvironment()Z
    at net.minecraft.util.SoundCategory.findField(SourceFile:574)
    at net.minecraft.util.SoundCategory.<clinit>(SourceFile:39)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.lang.Class.getEnumConstantsShared(Class.java:3320)
    at java.lang.System$2.getEnumConstantsShared(System.java:1249)
    at java.util.EnumMap.getKeyUniverse(EnumMap.java:752)
    at java.util.EnumMap.<init>(EnumMap.java:138)
    at com.google.common.collect.Maps.newEnumMap(Maps.java:481)
    at net.minecraft.client.settings.GameSettings.<init>(GameSettings.java:111)
    at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:443)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377)
    at net.minecraft.client.main.Main.main(SourceFile:123)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)