I get this error when writing to the database:
A dependent property in a ReferentialConstraint is mapped to a store-generated column. Column: \'Paym
This error says that you are using unsupported relation or you have error in your mapping. Your code is most probably absolutely unrelated to the error.
The error means that you have some relation between entities where foreign key property in dependent entity is defined as store generated. Store generated properties are filled in the database. EF doesn't support store generated properties as foreign keys (as well as computed properties in primary keys).