[AmgedIsmail]

Hello,
The subject is not "today" here. It refers to the birthday...
A: When is your birthday?
B: My birthday is September third.
A: Is it September sixth?

So, I am going to follow the correct grammar which is first comes the subject..

A: anata no tanjoubi wa itsu desu ka.
あなたのたんじょうびはいつですか。

B: watashi no tanjoubi kugatsu mikka desu.
わたしのたんじょうびくがつみっかです。

A: tanjoubi wa kugatsu mikka desu ka.
たんじょうびはくがつみっかですか。

But in the website, they didn't mention "your" in 1st A.
A: Tanjoubi wa itsu desu ka.

And they didn't mention "My " in B.
B: Tanjoobi wa kugatsu mikka desu.

And where is the subject in the 2nd A.
The website's answer is:
A: kugatsu mikka desu ka.

So, is any of my answers wrong, please?