It's my understanding that where you ecievereceive your handset via a network provider, you're likely to be unable to access the UI8.5 Beta program. The reason for this is because your network provider will usually:
Ensures the update is compatible, stable, and won't negatively affect their network's services, like voice calls, data connectivity, or specific carrier-added features (e.g., Wi-Fi calling settings).
Manufacturer (Google, Samsung, Apple, etc.) creates and tests the update. Carrier (Verizon, O2, EE, etc.) receives the update, conducts their own testing, and may apply network-specific customizations. Carrier approves and then begins the Over-The-Air (OTA) rollout to devices on their network.
Therefore interfere with the Beta program.