Travelling to Ireland with baby

I am a Pakistani citizen intending to travel to Republic of Ireland on a Short Stay visa category. This time my daughter will also travel with me. She has a British passport and is a British Citizen. She is 2 months old.

On my visa application form I entered that 1 dependent child will travel with me and this child has British citizenship and that this child will travel using own passport. But I get this message "A separate online Visa/Preclearance application must be completed for each dependent intending to travel whether they hold their own passport or are included on yours. A Visa/Preclearance processing fee is payable for each individual application"

Why does my daughter need to make a visa application in spite of being a UK citizen and being only 2 months old? I do not comprehend.

She doesn't need a visa. You could have left her information off the form.