Celery chord issue

tasks.py

# tasks.py
from celery import task, Celery, subtask, group
import time

REDIS_SERVER = 'redis://localhost:6379'

celery = Celery("app", broker=REDIS_SERVER, backend=REDIS_SERVER)

@task()
def task1(input):
    time.sleep(1)
    return "task1 " + input

@task()
def task2(input):
    time.sleep(1)
    return "task2 " + input

@task()
def task3(input):
    time.sleep(1)
    return "task3 " + input

@task()
def dmap(it, callback):
    # Map a callback over an iterator and return as a group
    callback = subtask(callback)
    return group(callback.clone([arg,]) for arg in it)()
    
    
    
# run.py
from celery import chord
import tasks

params = ["A","B","C","D"]

task_1 = (tasks.task1.s(p) for p in params)
task_2 = (tasks.dmap.s(tasks.task2.s()))
task_3 = tasks.task3.s()

workflow = chord([task_1, task_2])(task_3)