Here are a few potential causes and solutions for the 400 Bad Request error that occurs after a day:
Token Expiry: Ensure that your authentication tokens are being refreshed properly. If the token expires after a day, it could lead to a 400 error.
Data Limits: Copilot Studio limits connector responses to 500 KB. If your request returns too much data, it might cause a 400 error. Try filtering the data to reduce the response size.
Configuration Issues: Double-check your SSO and connector configurations. Any misconfiguration could lead to authentication errors.
Network Issues: Intermittent network issues can also cause 400 errors. Ensure your network connection is stable and there are no firewall rules blocking the requests.