The owner of the ClientID is irrelevant.
It’s all about whom authenticates/grant access to the clientID
The user you want to read, STREAMER_ID needs to authenticate.
Here you are using implicit auth which means that when you send this page to someone else, they login and only have access to their own rewards/redemptions on their channel as you are only operating as that user.
You cannot read USERB redemptions when you are logged in as USERA in your code.
So here, you are potentially running the wrong authentication type, since there is no way to store the token somewhere else for your usage.
Normally you would create a portal, that uses your ClientID, that uses regular oAuth, to get permission/a token from STREAMER_ID store that token on your server.
Then when your script that needs to do things with redemptions would load and use that token (refresh if needed)