How to save entities dependent on others with JPA (Java Persistence API)?

I am currently developing an api-rest with spring-boot, whose services will be called from an application in angular, the SQL server is being used as database manager. I have the following tables:

I am capturing the data of an insured, through a form in angular

The relationship I have between these two entities is one by one, an Insured is a person, so I have defined their classes:

INSURED

import javax.persistence.*;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import java.sql.Time;
import java.util.Date;

@Entity
@Table(name = "Assureds")
@Access(AccessType.FIELD)
public class Assured extends ParentEntity {

    private static final long serialVersionUID = -5015666908034563954L;

    public Assured() {
        super();
    }

    @Column(name = "Assuredtype_Id", nullable = true) 
        private Integer assuredtypeId;    

    @Column(name = "Person_Id", nullable = false) 
    private int personId;

    @Column(name = "Applicantnumber", nullable = true) 
    private Integer applicantNumber;

    @Column(name = "Deceaseddate", nullable = true)
    private Date deceasedDate;

    @Column(name = "Deceasedlocality", nullable = true)
    private String deceasedLocality;

    @Column(name = "Since", nullable = true) 
    private Time since;

    @Column(name = "Until", nullable = true) 
    private Time until;

    /*Un asegurado es una persona */
    @OneToOne(cascade= {CascadeType.ALL})
    @JoinColumn(name="Person_Id", referencedColumnName="id", insertable = false, updatable = false)
    public Person person;



    public Integer getAssuredtypeId() {
        return assuredtypeId;
    }

    public void setAssuredtypeId(Integer assuredtypeId) {
        this.assuredtypeId = assuredtypeId;
    }

    public int getPersonId() {
        return personId;
    }

    public void setPersonId(int personId) {
        this.personId = personId;
    }

    public Integer getApplicantNumber() {
        return applicantNumber;
    }

    public void setApplicantNumber(Integer applicantNumber) {
        this.applicantNumber = applicantNumber;
    }

    public Time getSince() {
        return since;
    }

    public void setSince(Time since) {
        this.since = since;
    }

    public Time getUntil() {
        return until;
    }

    public void setUntil(Time until) {
        this.until = until;
    }

    public AssuredType getAssuredtype() {
        return assuredtype;
    }

    public void setAssuredtype(AssuredType assuredtype) {
        this.assuredtype = assuredtype;
    }

    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }

    public Date getDeceasedDate() {
        return deceasedDate;
    }

    public void setDeceasedDate(Date deceasedDate) {
        this.deceasedDate = deceasedDate;
    }

    public String getDeceasedLocality() {
        return deceasedLocality;
    }

    public void setDeceasedLocality(String deceasedLocality) {
        this.deceasedLocality = deceasedLocality;
    }

}

PERSON

import java.util.Date;
import java.util.List;
import javax.persistence.*;

@Entity
@Table(name = "Persons")
@Access(AccessType.FIELD)

public class Person extends ParentEntity {

    private static final long serialVersionUID = -5015666908034563954L;

    public Person() {
        super();
    }


    @Column(name = "Name", nullable = false) 
    private String name;    

    @Column(name = "Lastname", nullable = false) 
    private String lastName;    

    @Column(name = "Picture_Id", nullable = true) 
    private Integer pictureId;

    @Column(name = "Dni", nullable = false, length = 255)
    private String dni;  

    @Column(name = "Email", nullable = false, length = 255) 
    private String email;

    @Column(name = "Nationality", nullable = true, length = 255) 
    private String nationality;

    @Column(name = "Birthdate", nullable = true, length = 255) 
    private Date birthDate;

    @OneToOne(mappedBy="person")
    private Set<Assured> assured;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Integer getPictureId() {
        return pictureId;
    }

    public void setPictureId(Integer pictureId) {
        this.pictureId = pictureId;
    }

    public FileUpload getFileUpload() {
        return fileUpload;
    }

    public void setFileUpload(FileUpload fileUpload) {
        this.fileUpload = fileUpload;
    }

    public String getDni() {
        return dni;
    }

    public void setDni(String dni) {
        this.dni = dni;
    }

    public Gender getGender() {
        return gender;
    }

    public void setGender(Gender gender) {
        this.gender = gender;
    }

    public List<Phone> getPhones() {
        return Phones;
    }

    public void setPhones(List<Phone> phones) {
        Phones = phones;
    }

    public List<Address> getAddresses() {
        return this.Addresses;
    }

    public void setAddresses(List<Address> addresses) {
        this.Addresses = addresses;
    }

    public void setAddress(Address address) {
        Addresses.add(address);
    }
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getNationality() {
        return nationality;
    }

    public void setNationality(String nationality) {
        this.nationality = nationality;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }


}

PARENTENTITY

import java.io.Serializable;
import javax.persistence.Access;
import javax.persistence.AccessType;
import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import javax.persistence.GenerationType;

@MappedSuperclass
@Access(AccessType.FIELD)
public class ParentEntity implements Serializable{


    private static final long serialVersionUID = -2890482081142183458L;
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id", unique = true, nullable = false)

    private Integer id;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

}

And this is my controller where I define the urls

import java.io.IOException;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

@RestController
public class AssuredController {
    @Autowired
    protected AssuredService assuredService;
    protected ObjectMapper mapper;

     @CrossOrigin(origins = "*")
    @RequestMapping(value = "/api/assured/saveOrUpdate",method = RequestMethod.POST)
    public RestResponse saveOrUpdate(@RequestBody String assuredJSON) throws JsonParseException, JsonMappingException, IOException {
        this.mapper= new ObjectMapper();
        Assured assured= this.mapper.readValue(assuredJSON,Assured.class);
        this.assuredService.save(assured);
        return new RestResponse(HttpStatus.OK.value(), "Operacion Exitosa");
    }
    @RequestMapping(value = "/api/assured/getAll", method = RequestMethod.GET)
    public List<Assured> getAll() {
        return this.assuredService.findAll();
    }
    @RequestMapping(value = "/api/assured/delete", method = RequestMethod.POST)
    public void deleteUser(@RequestBody String assuredJson) throws Exception {
        this.mapper = new ObjectMapper();

        Assured assured = this.mapper.readValue(assuredJson, Assured.class);

        if (assured.getId()==0) {
            throw new Exception("El id esta nulo");
        }
        this.assuredService.delete(assured.getId());
    }
}

REPOSITORY

package dao;

import org.springframework.data.jpa.repository.JpaRepository;
import com.sotec.BestLegalAssistance.model.Assured;

public interface AssuredRepository extends JpaRepository<Assured, Integer>{
    @SuppressWarnings("unchecked")
    Assured save(Assured assured);
    void delete(int id);
}

** The api saves, removes and edits perfectly when I send the entities separately, that is, I capture the data of the person, I save it, I create a method to bring the saved person, I take out his id and proceed to save the insured with the id of the person I brought. I've been studying spring for 1 month as such, I'm a novice.

What I want to do is send you from the front-end the insured data with your personal object, and believe me the two entities in a single request, knowing that an insured has a foreign key of the person Id. When I try to insert the insured I get an error in the java console saying that the person_id can not be null, so I see, the person does not believe me and when he tries to save the insured does not find the Person_ID.

I do not know if you can do what I ask, I have documented with respect to the subject but I do not get an example to help implement it **