[EF Core 8] Many-to-many relationship with payload

public class Post
{
    public int Id { get; set; }
    public List<Tag> Tags { get; } = new();
    public List<PostTag> PostTags { get; } = new();
}

public class Tag
{
    public int Id { get; set; }
    public List<Post> Posts { get; } = new();
    public List<PostTag> PostTags { get; } = new();
}

public class PostTag
{
    public int PostId { get; set; }
    public int TagId { get; set; }
    public string CustomPayload { get; set; }
}

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options) { }
    public virtual DbSet<Post> Posts { get; set; }
    public virtual DbSet<Tag> Tags { get; set; }
}

Unable to create a 'DbContext' of type ''. The exception 'The entity type 'PostTag' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'

Unable to create a 'DbContext' of type ''. The exception 'Cannot use table 'PostTag' for entity type 'PostTag' since it is being used for entity type 'PostTag (Dictionary<string, object>)' and potentially other entity types, but there is no linking relationship. Add a foreign key to 'PostTag' on the primary key properties and pointing to the primary key on another entity type mapped to 'PostTag'.