Can`t use Mixin

[Artemisia-Elre]

I want to make extensions of this mod for my modpack,but when i use mixin to AbstractSpell.class and build. Return Errors

����: Unable to locate obfuscation mapping for @shadow field
@shadow protected int baseManaCost;
^
����: Unable to locate obfuscation mapping for @shadow field
@shadow protected int manaCostPerLevel;
^
����: Unable to locate obfuscation mapping for @shadow method
@shadow public abstract int getLevel(int level, @org.jetbrains.annotations.Nullable LivingEntity caster);
^
����: Unable to locate obfuscation mapping for @overwrite method
public int getManaCost(int level, @nullable LivingEntity caster) {
^

import io.redspace.ironsspellbooks.api.spells.AbstractSpell;
import io.redspace.ironsspellbooks.config.ServerConfigs;
import net.minecraft.world.entity.LivingEntity;
import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.Overwrite;
import org.spongepowered.asm.mixin.Shadow;

import javax.annotation.Nullable;

@mixin(AbstractSpell.class)
public abstract class AbstractSpellMixin {
@shadow protected int baseManaCost;

@Shadow protected int manaCostPerLevel;

@Shadow public abstract int getLevel(int level, @org.jetbrains.annotations.Nullable LivingEntity caster);

/**
 * @author
 * @reason
 */
@Overwrite
public int getManaCost(int level, @Nullable LivingEntity caster) {
    return (int)((double)(this.baseManaCost + this.manaCostPerLevel * (this.getLevel(level, caster) - 1)) * ServerConfigs.getSpellConfig((AbstractSpell) (Object)this).manaMultiplier());
}

}