I first time use sequelize. I define two models but after run show error. I dont know how to fix this. help me please. GalleryType model:

const GalleryType = sequelize.define("gallerytype",{
    _id: {
        type: DataTypes.INTEGER,
        autoIncrement: true,
        allowNull: false,
        primaryKey:true
    },
    title:{
        type: DataTypes.STRING,
        allowNull: false,
        
        unique: {
            arg:true,
            name: 'Unique field',
            msg: "Gallery type must be unique"
        }
    }
})
GalleryType.hasMany(Gallery, {foreignKey: 'type', onDelete: 'CASCADE'})

Gallery model:

const Gallery = sequelize.define("gallery",{
    _id: {
        type: DataTypes.INTEGER,
        autoIncrement: true,
        allowNull: false,
        primaryKey:true
    },
    title:{
        type: DataTypes.STRING,
        allowNull: false
    },
    picture: DataTypes.STRING,
    url:{
        type: DataTypes.STRING,
        allowNull: false
    }
})
Gallery.belongsTo(GalleryType, {foreignKey: 'type'})

Error: gallery.belongsTo called with something that's not a subclass of Sequelize.Model