Smart parental controls - "This plan is not available"

I'd try first to update the RBS then RBR lastly:

https://community.netgear.com/t5/Orbi-Wi-Fi-5-AC-and-Orbi-with/New-RBR50-RBS50-Firmware-Version-2-7-5-4/td-p/2296598/jump-to/first-unread-message

Then factory reset using:

https://kb.netgear.com/000062081/How-do-I-erase-the-configuration-settings-on-my-Orbi-WiFi-System

Then setup from scratch using a PC and web browser first, don't use Orbi app:

https://kb.netgear.com/22697/How-do-I-install-my-NETGEAR-router-using-the-router-web-interface
Recommend setting the default DHCP IP address pool range to the following after applying and a factory reset: 192.168.#.100 to 192.168.#.200.
https://kb.netgear.com/24089/How-do-I-specify-the-pool-of-IP-addresses-assigned-by-my-Nighthawk-router

Once the system is setup, then log into the Orbi app and see if you can check your subscription using the 3 horizonal lines top left corner of the app to show menu list and see if Subscriptions is listed there and check status or see if it directs you to the SPC subscription or any Circle subscriptions? 

You may need to contact NG support for help and information regarding subscriptions as this is beyond forum help:

https://community.netgear.com/t5/NETGEAR-Smart-Home-Parental/Smart-Parental-Controls-Help-and-Information/td-p/2193919/jump-to/first-unread-message

https://community.netgear.com/t5/Circle-Smart-Parental-Controls/Circle-Pass-Code-Help-and-Information/td-p/2192590/jump-to/first-unread-message

KevinLiT