Why cannot run in dynmno with IN0,1,2

Revit
1 
import sys
import clr

# Import Revit API
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *

# Import Revit Services (for Dynamo)
clr.AddReference('RevitServices')
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager

# Import DesignScript Geometry (for Dynamo)
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *


def substitute_material_appearance(element, source_material_name, target_material_name):
    # Get Revit document
    doc = DocumentManager.Instance.CurrentDBDocument

    # Get the source and target materials
    materials = FilteredElementCollector(doc).OfClass(Material)
    source_material = None
    target_material = None

    for material in materials:
        if material.Name == source_material_name:
            source_material = material
        if material.Name == target_material_name:
            target_material = material
        if source_material and target_material:
            break

    if source_material is None or target_material is None:
        missing_materials = []
        if source_material is None:
            missing_materials.append(f"Source material '{source_material_name}' not found.")
        if target_material is None:
            missing_materials.append(f"Target material '{target_material_name}' not found.")
        raise Exception("\n".join(missing_materials))

    # Substitute appearance settings from source_material to target_material
    source_appearance_asset_id = source_material.AppearanceAssetId
    source_appearance_asset_elem = doc.GetElement(source_appearance_asset_id)

    # Start a transaction (required for modifying the document)
    TransactionManager.Instance.EnsureInTransaction(doc)

    # Assign the source material's appearance asset to the target material
    target_material.AppearanceAssetId = source_appearance_asset_id

    # Commit the transaction
    TransactionManager.Instance.TransactionTaskDone()

    return "Material appearance substituted successfully."


# The inputs to this node will be stored as a list in the IN variables.
dataEnteringNode = IN

if len(dataEnteringNode) < 3:
    OUT = "Error: Please provide an element and both source and target material names as inputs."
else:
    element = UnwrapElement(IN[0])  # Unwrap the element to access the Revit element
    source_material_name = IN[1]
    target_material_name = IN[2]

    try:
        result = substitute_material_appearance(element, source_material_name, target_material_name)
        OUT = result
    except Exception as e:
        OUT = str(e)
2

You’re not declaring your variables. The first line, dataEnteringNode = IN, is telling you that inputs for the node are defined by IN. A specific input is then defined by the port it’s using, i.e. IN[0], IN[1], IN[2].