使用YouTube Data API获取频道播放列表时遇playlistNotFound错误

我正在开发一个项目，使用Python3和YouTube Data API，通过频道的旧用户名（legacy username）及forUsername参数获取频道的上传播放列表ID，进而获取频道内的视频及所需信息。部分频道可正常运行，但部分频道会返回playlistNotFound错误——即便我打印确认获取到的playlistId无误。以ManchesterUnited频道的播放列表ID UUNbg-_aV3kK4MEb2vgdBtsw 为例，报错信息如下：

googleapiclient.errors.HttpError: <HttpError 404 when requesting https://youtube.googleapis.com/youtube/v3/playlistItems?part=snippet&playlistId=UUNbg-_aV3kK4MEb2vgdBtsw&maxResults=50&key=AIzaSy...&alt=json returned "The playlist identified with the request's <code>playlistId</code> parameter cannot be found.". Details: "[{'message': "The playlist identified with the request's <code>playlistId</code> parameter cannot be found.", 'domain': 'youtube.playlistItem', 'reason': 'playlistNotFound', 'location': 'playlistId', 'locationType': 'parameter'}]">

from scraper_api import ScraperAPIClient
import requests
import googleapiclient.discovery
import html
import gspread
from oauth2client.service_account import ServiceAccountCredentials
import json
username=input("what is the channel username? (go to page and then you will see in the url) ")
ytapi = requests.get("https://www.googleapis.com/youtube/v3/channels?part=contentDetails&forUsername="+username+"&key=AIzaSy...")
print(ytapi.text)
at=ytapi.text.split(' ')
c=1
b=0
viewnumbers = []
titles = []
vtypes = []
urls = []
for i in at:
    c+=1
    if 'uploads' in i:
        for it in at[c-3:]:
            if 'U' in it:
                print(it)
                idd=it[1:len(it)-2]
                print(idd)
                break

playlist_id = idd

youtube = googleapiclient.discovery.build("youtube", "v3", developerKey = "AIzaSy...")

request = youtube.playlistItems().list(
    part = "snippet",
    playlistId = playlist_id,
    maxResults = 50
)
response = request.execute()

内容的提问来源于stack exchange，提问作者Sean Cassidy