Cannot bind JSON in Golang Gin to struct with ManyToMany field - algorithm

Question

I have the following structs as relational models:
type Product struct {
ID uint32 `gorm:"primary_key;auto_increment" json:"id"`
Name string `gorm:"size:100;not null" json:"name"`
Description string `gorm:"size:512" json:"description"`
Price float64 `gorm:"default:0" json:"price"`
Shop Shop `json:"shop"`
ShopID uint32 `gorm:"not null" json:"shop_id"`
Categories []Category `gorm:"many2many:product_categories;" json:"categories"`
CreatedAt time.Time `gorm:"default:CURRENT_TIMESTAMP" json:"created_at"`
UpdatedAt time.Time `gorm:"default:CURRENT_TIMESTAMP" json:"updated_at"`
}
type Category struct {
ID uint32 `gorm:"primary_key;auto_increment" json:"id"`
Name string `gorm:"size:100;not null" json:"name"`
CreatedAt time.Time `gorm:"default:CURRENT_TIMESTAMP" json:"created_at"`
UpdatedAt time.Time `gorm:"default:CURRENT_TIMESTAMP" json:"updated_at"`
}
Now, on my controller I want to create a Product with multiple categories from a JSON object but I can't find a way on how to do it; thus, it returns the message Unable to bind data to product. Here is the code:
func (s *Server) createProduct(c *gin.Context) {
uid, err := auth.ExtractTokenID(c.Request)
if err != nil {
c.IndentedJSON(http.StatusUnauthorized, gin.H{"message": "Unauthorized"})
return
}
var product = models.Product{}
var shop = models.Shop{}
if err := c.BindJSON(&product); err != nil {
fmt.Println(err)
c.IndentedJSON(http.StatusInternalServerError, gin.H{"message": "Unable to bind data to product"})
return
}
Is there a solution or a simple way on how to achieve this? As I haven't been able to find anything on gorm documentation.
Edit; Here is the JSON object I'm sending:
{
"name": "Soap",
"description": "Smelly Soap",
"Price": 12.99,
"categories": [1]
}