One of the steps required to configure the JOIN Shopping feature is entering your Google Merchant ID. Here's where to find it.
1- Sign in to Google Merchant Center
2- Find your Merchant ID
Your Merchant ID is displayed in the top banner.
It is the number shown in the top-right corner, next to your company name.
"Unauthorized" error message
If you see this error when entering your Merchant ID in JOIN Studio, it means you are using a Google account that does not yet have access to your Merchant Center.
Follow this guide:
How to add a new user to your Merchant Center