WriteConflicts in mongo

from pymongo import MongoClient, ReadPreference, WriteConcern
from pymongo.read_concern import ReadConcern
from time import sleep
from threading import Thread
from dotenv import dotenv_values

config = dotenv_values(".env")

def first_transaction():
    client = MongoClient(config["MONGO_URI"])
    db = client["test"]
    collection = db["transaction_test"]

    sleep(5)

    while True:
        try:
            with client.start_session() as session:
                session.start_transaction(
                    read_concern=ReadConcern(level="snapshot"),
                    write_concern=WriteConcern(w="majority"),
                    read_preference=ReadPreference.PRIMARY
                )

                doc = collection.find_one({"id": 1}, session=session)
                print(f"Thread 1 read value: {doc.get('value') if doc else None}")
                sleep(10)
                print("Thread 1 attempting write")
                result = collection.update_one({"id": 1}, {"$inc": {"value": -1}}, session=session)
                print(f"Thread 1 write result: {result.modified_count} modified")

                session.commit_transaction()
                print("Thread 1 committed transaction")

            sleep(5)
        except Exception as e:
            print(f"Thread 1 unexpected error: {e}")

def second_transaction():
    client = MongoClient(config["MONGO_URI"])
    db = client["test"]
    collection = db["transaction_test"]

    while True:
        try:
            print("Thread 2 attempting write")
            result = collection.update_one({"id": 1}, {"$inc": {"value": 2}})
            print(f"Thread 2 write result: {result.modified_count} modified")
            sleep(5)
        except Exception as e:
            print(f"Thread 2 unexpected error: {e}")

if __name__ == "__main__":
    print("Starting threads...")
    Thread(target=first_transaction).start()
    Thread(target=second_transaction).start()