GORM don't create many2many associations

I have model:

type Book struct {
	gorm.Model
	Title       string `json:"title"`
	Author      string `json:"author"`
	Description string `json:"description"`
	Category    string `json:"Category"`
	Publisher   string `json:"publisher"`
	AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard; "json:"authorscard"`
}

type AuthorsCard struct {
	gorm.Model
	Name        string `json:"name"`
	Age         int    `json:"age"`
	YearOfBirth int    `json:"year"`
	Biography   string `json:"biography"`
}

After db.AutoMigrate(&models.Book{}, &models.AuthorsCard{})
I have a creation function:

func TestCreate() {
	var testbook = models.Book{
		Title:  "Test",
		Author: "tst",
		AuthorsCard: []*models.AuthorsCard{
			{
				Age:         23,
				Name:        "test",
				YearOfBirth: 1999,
				Biography:   "23fdgsdddTEST",
			},
		},
		Description: "something",
	}
	db.Preload("AuthorsCard").Find(&models.Book{})

	db.Create(&testbook)

}

despite That AuthorsCard has some data in it, I receive this as a response:

{
        "ID": 78,
        "CreatedAt": "2022-06-23T13:10:58.01629+03:00",
        "UpdatedAt": "2022-06-23T13:10:58.01629+03:00",
        "DeletedAt": null,
        "title": "Test",
        "author": "tst",
        "description": "something",
        "Category": "",
        "publisher": "",
        "authorscard": null
    }

As you can see "authorscard" is null.

How can I save "authorscard" to the database?
I used Gorm + postgresql and also I sent a few request with postman, results are the same - Authors card is null

The code is working when it's called in the correct order:

func TestCreate() {
	db := getDB()
	db.AutoMigrate(&Book{}, AuthorsCard{})

	var testbook = Book{
		Title:  "Test",
		Author: "tst",
		AuthorsCard: []*AuthorsCard{
			{
				Age:         23,
				Name:        "test",
				YearOfBirth: 1999,
				Biography:   "23fdgsdddTEST",
			},
		},
		Description: "something",
	}

    // 1. Create your testbook.
	db.Create(&testbook)

    // 2. Store it into a variable:
	var b1 *Book
	db.Preload("AuthorsCard").Find(&b1)
    
	fmt.Println(b1.AuthorsCard[0].Age)
	fmt.Println(b1.AuthorsCard[0].Name)
	fmt.Println(b1.AuthorsCard[0].YearOfBirth)
	fmt.Println(b1.AuthorsCard[0].Biography)

}

prints:

> 23
> test
1999
23fdgsdddTEST

Also your JSON export might fail since you pass a pointer to AuthorCard and the marshalling not always works properly in those cases. However, GORM does the right job here.

Static check also gave me some hints here:

type Book struct {
	gorm.Model
	Title       string         `json:"title"`
	Author      string         `json:"author"`
	Description string         `json:"description"`
	Category    string         `json:"Category"`
	Publisher   string         `json:"publisher"`
	AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard" json:"authorscard"` // wrong space
}