Z-codes- are some billable?

The ICD10Data.com site says this about the bereavement Z-code;

• Z63.4 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes
• That makes me think I CAN bill it. The client's Mental Health benefit detail link(BCBS,Availity) says that marriage counseling(another Z-code) is NOT covered but doesn't mention bereavement counseling.
• Is there some unwritten rule about Z-codes that I don't know about?