What is the expiation for pregnancy via a foreign woman's ovum?

What is known as a surrogate mother, who carries a fetus from another woman's egg, has been declared impermissible by Islamic scholars. And whoever has done this must repent to Allah Almighty. There is no specific expiation for this sin. As for the child, his real mother is the owner of the egg, and the owner of the womb is a legal mother, similar to a mother through suckling.