Why are some metrics greyed out when selecting metrics to sync between Influ2 and HubSpot?

Greyed-out metrics are properties that use a different field type within HubSpot. For example, Impressions = Number field type. So it can only be mapped to properties in HubSpot that were created with a 'Number' field type.

Follow this article to learn more about creating new properties within HubSpot for Influ2 metrics.