DBX027: A personal-data property has no subject
This page explains error DBX027 and how to fix it.
A [PersonalData] property has no subject: the event has no single [DataSubject] property, the named subject property is missing or not a string, or the subject ID is empty at append time.
Mark exactly one [DataSubject] string property, or name the subject with [PersonalData(Subject = "PropertyName")], and give it a value.