Python Request Loop Until Response Status Code 200

I'm trying to make a python loop unitl CHANNEL_1, CHANNEL_2, CHANNEL_3, CHANNEL_4. request response code 200

import requests
import time

USERS_TOKEN = "TOKEN"
MDICT = {"CHANNEL_1": "message_1",
         "CHANNEL_2": "message_2",
         "CHANNEL_3": "message_3",
         "CHANNEL_4": "message_4"
         }
msgcount = 10


def sendMessage(token, channel_id, message):
    url = f'https://discord.com/api/v9/channels/{channel_id}/messages'
    data = {"content": message}
    header = {"authorization": token}
    with requests.Session() as session:
        r = session.post(url, data=data, headers=header)
        r.raise_for_status()
        return r.status_code
        
while msgcount > 0 and MDICT:
    time.sleep(0.3)
    key = next(iter(MDICT.keys()))
    if sendMessage(USERS_TOKEN, key, MDICT[key]) == 200:
        del MDICT[key]
    msgcount -= 1