how can i retrieve object properties from the object returned from api calls using rest template - spring-boot

Question

i made an api call using spring rest template as a rest client. when the method that makes the api returns a string, postman is able to see the object and the associated object properties with its values. but when i change the return type to an object that models the api object returned, i get all null values. is there something wrong i'm doing?
#GetMapping(value="/verbvn/{xbvn}")
public Participant verBVN(#PathVariable String xbvn) {
System.out.println("bvn is "+xbvn);
HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
headers.setBearerAuth("sk_live_32a7ffd9cc47f");
HttpEntity <String> entity = new HttpEntity<String>(headers);
Participant r= restTemplate.exchange("https://api.stck.co/bnk/resolve_bvn/"+xbvn, HttpMethod.GET, entity, new ParameterizedTypeReference<Participant>() {}).getBody();
System.out.println("the participant firstname is "+r.getFirstName());
return r;
}
public class Participant {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column
private Long id;
#OneToOne(cascade=CascadeType.ALL)
#JoinColumn(name="id",referencedColumnName="id")
private Data data;
public Participant() {
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Data getData() {
return data;
}
public void setData(Data data) {
this.data = data;
}
}
#Entity
#Table
#Async
#JsonIgnoreProperties(ignoreUnknown=true)
public class Data {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column
private Long id;
#Column
#JsonProperty(value="first_name")
private String firstName;
#Column
#JsonProperty(value="last_name")
private String lastName;
#Column
#JsonProperty(value="phone")
private String phoneNumber;
#Column
#JsonProperty(value="email")
private String email;
public Data() {}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getPhoneNumber() {
return phoneNumber;
}
public void setPhoneNumber(String phoneNumber) {
this.phoneNumber = phoneNumber;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}