Add your id to your metadata
To moderate, you need to specify yourself as an administrator. To do this, simply include the open chart meta tags in the URL specified as the plugin's href parameter. These tags must be included in the document. Enable
<meta property="fb:admins" content="{YOUR_FACEBOOK_USER_ID}"/>
Same process for application id
If there are many comments on your site, we strongly recommend that you specify the Facebook application identifier as an administrator (all application administrators will be able to moderate comments). This allows you to use the moderator interface on Facebook, where the comments of all plugins controlled by your application ID can be easily combined together. You can specify either fb: app_id or fb: admins, but not both. This tag must be specified in.
<meta property="fb:app_id" content="{YOUR_APPLICATION_ID}"/>
All this in the document that you linked https://developers.facebook.com/docs/reference/plugins/comments/
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