1. In order to bring your custom conversions (pixel-based metrics) into Tableau using the Facebook Ads connector, all you have to do is select 'action_type' in the dimension field and 'actions' in the metric field.
2. Your custom conversion will be displayed as ‘offsite_conversion.custom.’, followed by a string of numbers representing your custom conversion ID, as shown below:
You'll find the conversion ID (to identify the custom conversion in Tableau) in your Facebook Ads.