To give sadqah instead of doing aqiqah
In the name of Allah, the most Beneficent, the most Merciful.
The performance of aqiqah is highly encouraged. It is to be performed by the parents or the guardian of the child.
The Prophet of Allah Sallallahu Alahi Wasalam has said that a child is pledged to its aqiqah which is sacrificed on behalf of the child on the seventh day when it is given a name and the hair is shaved off its head. (Sunan Tirmizi p.278 v.1)
Aqiqah should be performed on the seventh day of the birth of the child and if not done on the seventh day then whenever it is done, it should be on the next seventh day and so on. (Ibid)
One can do aqiqah until the child has reached the age of puberty after which it will be considered as a optional sacrifice. (Ahsanul Fatawa p.536 v.7)
With regards to your question if a person gives sadqah or the price of a goat instead of doing the actual sacrifice, the sunnah of doing aqiqah will not be performed.
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.