As M. Deinum correctly pointed out in the comments, the root cause is a property name mismatch between your frontend JSON and the backend Java class. Angular sends this (property name = address):

{
"customer": { ... },
"address": {
"street": "123 Main St",
"city": "Springfield",
...
},
"order": { ... },
"orderItems": \[ ... \]
}

But the Java Purchase class has:

private Address shippingAddress;   // ← Jackson looks for "shippingAddress"

Jackson (Spring's JSON deserializer) matches JSON property names to Java field names (or getter/setter names). Since there is no field/property called address, that part is ignored → shippingAddress remains null. Recommended Fix : Keep your Java field name as shippingAddress, but tell Jackson to map the incoming "address" to it:

@Data
public class Purchase {

    private Customer customer;

    @JsonProperty("address")           // ← this fixes it
    private Address shippingAddress;

    private Order order;

    private Set<OrderItem> orderItems;
}

Just add the @JsonProperty("address") annotation (from com.fasterxml.jackson.annotation.JsonProperty). This is the cleanest solution because:

• Your domain model stays meaningful (shippingAddress)

• You don't have to change the frontend

• The API contract is explicitly defined

Alternative Fixes If you prefer not to use @JsonProperty, you have two other options:

• Rename the Angular/TS property to match Java:

export class Purchase 
{ 
    customer!: Customer; 
    shippingAddress!: Address;   // ← now matches 
    order!: Order; 
    orderItems!: OrderItem[]; 
} 

• Rename the Java field to address:

private Address address;   // simple name

Then update any other places that reference shippingAddress.