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I am deploying a Flask application on Zeabur, but the app fails to start with the following error:

File "/app/config.py", line 12, in Config
raise ValueError("必须设置环境变量 SECRET_KEY")
ValueError: 必须设置环境变量 SECRET_KEY
Although I have explicitly set the SECRET_KEY environment variable in the service's Environment Variables page, the app does not seem to read it.

Project Details:

• Application type: Python Flask (using Flask-SQLAlchemy)
• Database: MySQL (created inside Zeabur)
• Deployment method: Direct folder upload via "Local Project"
• Code status:
• Modified config.py to dynamically build the database connection string using the auto-injected MYSQL_* variables (following community advice). The manually set DATABASE_URL variable has been deleted.
• Added debug print statements, but the app crashes before executing them.

Steps already taken:

1. Verified that SECRET_KEY exists and has the correct value in the Environment Variables page.
2. Clicked "Save" and redeployed multiple times – the issue persists.
3. Added a debug print in config.py right after reading the env var, but the app fails to reach that line.
4. Deleted and recreated the service several times, re-adding the environment variables each time – still the same error.

Latest logs (relevant part):

Screenshot of environment variables:
(I have attached a screenshot showing that SECRET_KEY is present, with its value redacted for security. The key is correctly set in the environment.))

Questions:

1. Why does the app fail to read SECRET_KEY even though it appears in the Environment Variables list?
2. How can I verify whether the environment variable is actually injected into the container?

Additional info:

• I am a paid user (已充值) and would appreciate a quick resolution.
• The project needs to go live as soon as possible. Thank you for your help!