在discord.py中，如何在刚创建的频道上发送消息？

我正在制作一个票务机器人，每当有人对“票务”类别中的消息做出反应时，它都会创建一个频道，如何获取频道obj，以便该机器人可以在那里发送消息？

我有这个：

@client.event
async def on_raw_reaction_add(payload):
    r_msg_id = payload.message_id
    print(r_msg_id)
    channel_id = payload.channel_id
    user_id = payload.user_id
    channel = client.get_channel(channel_id)
    category_id = int("719621258106372219")
    category = client.get_channel(category_id)
    client.get_channel(r_msg_id)
    msg_obj = await channel.fetch_message(r_msg_id)
    guild_id = payload.guild_id
    guild = client.get_guild(guild_id)
    member = payload.member
    f = open("ticket_nums.txt", "w+")
    #ticket_num = f.read()
    #f.write(int(ticket_num) + 1)
    #f.close()
    overwrites = {
        guild.default_role: discord.PermissionOverwrite(read_messages=False),
        payload.member: discord.PermissionOverwrite(read_messages=True)
    }
    if True: #r_msg_id == "720708414107287724": commented out because it doesn't work idk why
        if not user_id == "718528256365559829":
            await msg_obj.remove_reaction("\U0001f4e8", discord.Object(id=user_id))
            await category.create_text_channel(r"ticket#" , overwrites=overwrites) #mette i permessi alla persona che apre il ticket

同样在打开应该包含票证数量的ticket_nums文件时，它使我不断出现此错误：（每次尝试打开文件时都给出该错误）

Ignoring exception in on_raw_reaction_add
Traceback (most recent call last):
  File "C:\Users\giaco\AppData\Local\Programs\Python\Python37\lib\site-packages\discord\client.py", line 312, in _run_event
    await coro(*args, **kwargs)
  File "C:\Users\giaco\Desktop\Bot\Discord Bot\bot_discord.py", line 216, in on_raw_reaction_add
    f = open("ticket_nums.txt", "w+")
PermissionError: [Errno 13] Permission denied: 'ticket_nums.txt'