Is there really no way to sync custom fields from Bill.com to NS?

Hey Luis if you have the bill.com data already in your Warehouse then you can use a Hightouch to send custom fields to NS

Sorry I'm not a tech guy. Can you please elaborate on that?

I'll add my experience with Bill.com using their integration with NetSuite was only the native segments (Location/Department/Class) were supported, no ability to have custom fields/segments from Bill.com source to NetSuite