How to link an id received via AJAX there is a related entity - Spring Boot MVC

Question

When receiving data from POST (AJAX) I only receive the id from Category and validate the class Product the following error occurs:

Resolved [org.springframework.http.converter.Httpmessagenotreadableexception: JSON parse error: Cannot Construct instance of br.com.projectName.pedidos.model.Category (Although at least one Creator exists): no String-argument constructor/Factory method to deserialize from String value ('1'); nested Exception is com.fasterxml.Jackson.databind.exc.Mismatchedinputexception: Cannot Construct instance of br.com.projectName.pedidos.model.Category (Although at least one Creator exists): no String-argument constructor/Factory method to deserialize from String value ('1') at [Source: (Pushbackinputstream); line: 1, column: 76] (through Reference chain: br.com.projectName.pedidos.model.Product["Category"])]

Product (Model)

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private int id;

    @OneToOne
    @NotEmpty(message = "Selecione uma categoria para este Produto")
    private Category category;

    @Column
    @NotEmpty(message = "Insita um nome válido para este campo")
    private String name;

    @Column
    private boolean excluded = false;

    //getter and setters
}

Category (Model)

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private long id;

    @Column
    @NotEmpty(message = "Defina o nome da categoria")
    private String name;
    //getter  and setters
}

Productcontroller

When there is a request via ajax via Post it receives the data and validates it.

@PostMapping("newProduct/")
    public ResponseEntity<?> processFormProduct (@Valid @RequestBody Product product, BindingResult bindingResult) {
        AjaxResponse result = new AjaxResponse();
        
        Product productExists = productService.findByNameAndCategory(product.getName(), product.getCategory().getId());
        
        if (productExists != null) {
            bindingResult.rejectValue("name", "error.name", "Já existe um produto com esse nome na categoria seleciona");
        }

        if (bindingResult.hasErrors()) {
            return ResponseEntity.badRequest().body(bindingResult.getAllErrors());
        } else {
            productService.saveProduct(product);

            result.setMsg("Produto cadastrado com sucesso!");
            result.setType("create");
            return ResponseEntity.ok(result);
        }
    }

Javascript script for AJAX request

$("#productForm").submit(function (event) {
    event.preventDefault();
    
    $(".validation-message").css("display", "block").html("");
    
    $.ajax({
        type: "POST",
        contentType: "application/json",
        url: $(this).attr("action"),
        data: JSON.stringify($(this).serializeJSON()),
        dataType: 'json',
        cache: false,
        success: function (data) {
            if(data.type=="create"){
                window.location.href = "/admin/produtos/?added=true";
            }else{
                window.location.href = "/admin/produtos/?updated=true";
            }
        },
        error: function (e) {
            var obj = Object.assign({}, e.responseJSON);
            Object.keys(obj).forEach(function(item){
                var field = obj[item].field;
                var label = $($("input[name='"+field+"']").next(".validation-message"));
                var msg = obj[item].defaultMessage;
                if($(label).html()==""){
                    $(label).css("display", "block").html(msg);
                }else{
                    $(label).append(", " + msg);
                }
                
            });
        }
    });
});

Formúlario (New Product)

<form id="productForm" th:action="@{/admin/produtos/newProduct/}" th:object="${product}" method="post">
    <div class="form-row">
        <div class="form-group col-md-6">
            <label for="inputNome" class="col-form-label">Nome</label>
            <input type="text" class="form-control" id="inputNome" th:field="*{name}"
                placeholder="Buquês">
        </div>
        <div class="form-group col-md-6">
            <label for="selCategoria" class="col-form-label">Categoria</label>
            <select id="selCategoria" class="form-control" th:field="*{category}">
                <option th:value="null" selected>Selecione...</option>

                <option th:each="categ : ${categorys}" th:value="${categ.id}" th:text="${categ.name}" ></option>
            </select>
        </div>
    </div>
    <button type="submit" class="btn btn-primary">Cadastrar</button>
</form>