How to reproduce:
1. Create or open a Unity project
2. Install the Splines (com.unity.splines) package
3. Create an empty GameObject inside the Hierarchy window
4. Add a “Spline Container” component to the newly created GameObject
5. Press the “?” button in the Inspector window within the “Spline Container” component
6. Observe the browser window

Actual result: “Sorry... that page seems to be missing!” shows up
Expected result: Documentation page is displayed without errors

Reproducible with: 2.7.2 (6000.5.0a5), 2.8.2 (6000.0.66f1, 6000.3.5f1, 6000.4.0b5, 6000.5.0a5)

Reproducible on: macOS 26.2 (M1 Max)
Not reproducible on: No other environments tested

Note: The opened link is https://docs.unity3d.com/6000.4/Documentation/Manual/script-SplineContainer.html (when using 6000.4.0b5)