Domain subscription was created on PBA-E side, but DNS hosting for this subscription was not created on POA side.
DNS hosting subscription will be created on POA side only if Name Servers Source Type is set to Get Name servers automatically in service template configuration for the domain.
Home>Products>Service Plans>Service Templates>[domain template] in PBA-E 5.5 or
Home>Product Director>Plan Manager>Service Templates>[domain template] in PBA-E 5.4 click
Edit and set Name Servers Source Type to Get Name servers automatically.