Review the screenshot of the configured field mappings for a sync between HubSpot and Mailchimp. How can you start segmenting the Mailchimp audience based on company size (number of employees)?

Everything is OK in PieSync. The segmentation on company size needs to be set up in Mailchimp directly.
The field mapping is not yet complete. The company size property still needs to be mapped to a custom field in Mailchimp.
It’s not possible to set up this type of segmentation through PieSync.

The correct answer is:

The field mapping is not yet complete. The company size property still needs to be mapped to a custom field in Mailchimp.