public class Packets {
		private static final String PROTOCOL_VERSION = "1";
		public static final SimpleChannel INSTANCE = NetworkRegistry.newSimpleChannel(
		    new ResourceLocation(CrudeTechMod.MOD_ID, "main"),
		    () -> PROTOCOL_VERSION,
		    PROTOCOL_VERSION::equals,
		    PROTOCOL_VERSION::equals
		);
		public static int i=0;
}

 

This is the handler of the packet sent

public static void handle(key msg, Supplier<NetworkEvent.Context> ctx) {
		ctx.get().enqueueWork(() -> {
			ServerPlayerEntity sender = ctx.get().getSender();
			ItemStack feet = ctx.get().getSender().getItemStackFromSlot(EquipmentSlotType.FEET);
            feet.damageItem(1, sender, player -> {});
		});
	ctx.get().setPacketHandled(true);
}

 

This is where the packet is sent
 

@SubscribeEvent
public static void onInput(InputEvent.KeyInputEvent event) {
	Packets.INSTANCE.sendToServer(new key(0));
}

I've removed some stuff to make it easier to read. Also, the handle is being run because I put a logger in it and it logged stuff

Since you're using a key to damage the item, I assume you're in creative. If so, the first line of ItemStack#damageItem should answer your question.

if (!entityIn.world.isRemote && (!(entityIn instanceof PlayerEntity) || !((PlayerEntity)entityIn).abilities.isCreativeMode))

 

oh no, key is just what I called the packet

But yes you are correct, I entered creative to test it, but didn't realize that ItemStack#damageItem doesn't damage in creative!
Thanks!