Hey Dotcomr,
We'd be happy to help out. Great job attempting to reactivate iMessage for use on the recovery contact's device, however there is new software available for their device, so let's get started by going ahead and updating to iOS 16.2 and testing things out a bit further using these steps:
Update your iPhone or iPad wirelessly
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.

5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
This is outlined further here: Update your iPhone or iPad
We hope this helps out, but if not, there's more info on adding a recovery contact available at the resource linked to your post above.
Take care!