Hi, i have just noticed that my mavic air 2 has a little fissure

Its quite small but i dont want it to get bigger and i report to repair service as it is under warranty, and of course there hasnt been any accident or hit

Fairly common problem here. Do a search for cracks in shell. Some have had good luck getting DJI to fix it under warranty. You'll just have to reach out to them. Ebay sells the shell for replacement, not a hard fix at all if you need to do it yourself. I have heard there is a slightly darker tone to the replacement shell. Don't know that for sure.

That looks like a simple scratch to me.

In another place it would be a simple scratch, but not just right there, in the axle. I think its produced by open and close the wings

I will report to Dji service. Thanks to all

Hello there. I am sorry to read and to know the issues that you are having with your DJI Mavic Air 2 and thank you for reaching out. Since there are cracks on the said DJI drone the best thing you need to do is to contact DJI Support at https://www.dji.com/support?site=brandsite&from=nav for us to be able to check the said DJI drone and for us to assist help you with this issue. It is not recommended to fly the said drone if these are stress crack on it. This cracks might affect the performance of the said drone while on flight and may lead to an unwanted incident. Again, I am sorry for the trouble and thank you for your understanding.

Hard to judge from a picture if it is a scratch or a crack.
Both are possible.