Hi @Kurt, in my experience PHP 8.1 has been the cause of most issues like this. I haven’t been able to replicate this error message, however I’ve put in a change to the code that should fix this and also fix the issue at Error during customer checkout via PayPal (which I also couldn’t replicate).
Can you try reinstalling the main Backlight modules by clicking ‘Reinstall’ under ‘Backlight’ on the Backlight modules page?