Cannot connect to Database - if via os.get and .env

This concerns many courses:

I get keys via dotenv and os.getenv. from .env
It works for my openai_api_key: "openai_api_key = os.getenv('OPENAI_API_KEY')" - and use it whenever it's required.

But I don't manage to get it working for Neo4j:
url = os.getenv('URL')
username = os.getenv('USERNAME')
password = os.getenv('PASSWORD')

Neither for Neo4jVector.from_documents, Neo4jVector.from_existing_index, Neo4jGraph...
When I use bolt://34.234.223.41:7687, neo4j, east-rubber-retailer (or similar data - all valid) directly it works.

What am I doing wrong?

Addendum: is it possible via .toml?