## Summary
We encountered a 403 Forbidden error when attempting to retrieve the membership subscriber list (`Members.list`) from YouTube Data API v3 using the `youtube.channel-memberships.creator` scope. The root cause was **products approval prerequisites and OAuth scope limitations**. Even with valid authorization credentials, **YouTube enforces strict eligibility requirements**.
## Root Cause
The failure occurred due to failing eligibility checks enforced by YouTube’s API:
- **Missing API product approval**: The `youtube.channel-memberships.creator` scope requires advanced permissions subject to manual review by Google. This wasn’t granted.
- **Insufficient channel eligibility**: For access to membership data, the channel must:
- Belong to an established YouTube Partner Program (YPP) account
- Have ≥ 1,000 subscribers
- Explicitly enable channel memberships in YouTube Studio
- **Inadequate scope validation**: The OAuth flow succeeded without confirming if the channel actually qualified for the requested resource.
## Why This Happens in Real Systems
This is commonplace in platforms with tiered access policies大力发展：
- **Permission gates**: APIs serving monetization or subscriber data often implement discretionary access controls not visible during development.
- **Silent consent failure**: OAuth authorization grants scopes immediately but fails at runtime if prerequisites aren’t met.
- **Multi-tiered enablement**: Resources requiring backend feature flags (e.g., channel memberships) often decouple consent from operational readiness.
## Real-World Impact
Business consequences included：
- **Blocked feature launch**: The membership web app couldn’t proceed without subscriber data.
- **User trust erosion**: Creators saw partial functionality ("auth success" but no data) during testing.
- **Project delay**: 48+ hours lost diagnosing undocumented eligibility constraints.
## Example or Code (if necessary and relevant)
```python
# Minimal valid GET request (
