That is great!
I have been in discussions about this and there are many that really believe that you can tell the gender of an embryo based on the egg shape. There are those both on BYC and online that sell eggs this way too. Often my posts are not directly in response to the person posting. These posts are read by a lot of people. If you google this topic, our posts from yesterday and today will come up high on the search.
I wanted to make sure that it was understood that this absolutely does not work. In order for any method to work for telling gender, you need to get above the coin flip level of results. That would be in the 90% correct range over thousands of eggs.
As an additional caution, There are a lot of bad eggs(pun!) out there in the poultry world. They have been around for a long time but with the current chicken fad going on there are a lot more. Beware of people on ebay selling Greenfire line hatching eggs. There really is no such thing. Once a person starts selling their own eggs, they are on longer from the original breeder and many of these breeders do not really have what you think you have. This is especially true for exotic breeds like ayam cemani.
They call a lot of these breeders "Straw Men". Often they are reselling hatchery eggs and chicks.
Be careful out there!