API access blocked (OAuthException code 200) for long-lived user token (FACEBOOK)

I'm running into an issue when trying to fetch data from a Facebook ad account via the Marketing API.

• I’m using a long-lived user access token created by the account admin.
• The user associated with the token has full access in Business Manager.
• Previously, the request /me/adaccounts worked and returned active accounts, but now it returns the error:

{'error': {'message': 'API access blocked.', 'type': 'OAuthException', 'code': 200, 'fbtrace_id': 'ANGfnFiboGN3X77OVXvprlu'}}

Example code causing the error:

import requests

access_token = "..." 
url = "https://graph.facebook.com/v23.0/me/adaccounts" 
params = {"access_token": access_token} 
response = requests.get(url, params=params) 
print(response.json())

I also tried fetching dashboard data via /insights for a specific ad account, but get the same error:

import requests, json, pandas as pd

access_token = "..."
ad_id = "act_7167..."

url = f"https://graph.facebook.com/v23.0/{ad_id}/insights"
time_range = json.dumps({"since":"2025-01-01","until":"2025-09-01"})

params = {
    "access_token": access_token,
    "time_range": time_range,
    "level": "ad",
    "fields": "date_start,date_stop,spend,impressions,frequency,cpc,ctr",
    "breakdowns": "country",
    "time_increment": 1
}

response = requests.get(url, params=params)
data = response.json()
if "error" in data:
    print("Error:", data["error"])
else:
    df = pd.DataFrame(data["data"])
    print(df.to_string())

Why does a valid long-lived user token still fail for /me/adaccounts and /insights?