migrations add выдаёт ошибку

когда делаю migrations выдаёт такую ошибку

Unable to determine the relationship represented by navigation property 'Phone.Purchase' of type 'Purchase'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

как исправить эту ошибку?

Models:

public class Phone 
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Producer { get; set; }
        public string LongDescription { get; set; }
        public int Price { get; set; }
        public string ImageName { get; set; }
        public byte[] Image { get; set; } 
        public string ImageUrl { get; set; }
        public int PurchaseId { get; set; }
        public Purchase Purchase { get; set; }
    }
public class Purchase 
    {
        public int PurchaseId { get; set; }
        public string Country { get; set; }
        public string City { get; set; }
        public Phone Phone { get; set; }
        public List<Phone> Phones { get; set; }
    }