The API key used for synchronizing Magento with Remarkety is actually stored in 2 different places in Magento:
1. As the password for the Remarkety XML-RPC user we use to pull the data into Remarkety, and
2. In Magento's configuration table, to be used when pushing data to Remarkety (subscribers and product price changes).
The two keys may become out of sync, and you'll be presented with an error message in the plugin. To fix this:
1. Click "Save" in the Magento plugin. This will override the existing XML-RPC user's password with the API key shown.
2. Log into Remarkety, go to Account Settings -> Connection Settings and enter this API key in the "API Connection Code" box. Click "Test Connection" and once you get a success message, click Save. If this doesn't work, contact support.
Note: If you are running a multi-store or multi-view Magento installation, you need to update the same key for all the Remarkety accounts which synchronize with this server.