Is it obligatory to fast in atonement for someone who used to masturbate during Ramadan, being ignorant of its prohibition and whether it nullifies the fast?

We congratulate you on being guided [to the truth] and ask God to accept your repentance and make you steadfast. Masturbation is forbidden, and its sin is more severe in Ramadan. It does not invalidate the fast unless semen is discharged. If no semen was discharged from you, then your fast is valid, and there is no make-up or expiation upon you. Some scholars are of the view that the fast is not invalidated by masturbation for someone ignorant of its prohibition. As for the missed prayers, they must be made up. If you do not know their number, continue making them up until you are reasonably certain that you have fulfilled your obligation.