Is it obligatory to make up or offer expiation for someone who masturbated during the daytime in Ramadan out of ignorance, and then repented from that?

You must repent to Allah and make up for the days you broke your fast due to masturbation. In addition, you must offer expiation for delaying the making up of those days until another Ramadan, which is to feed one poor person a "mudd" of food (approximately 750 grams) for each day. If you do not know the exact number of days, then make up for what you believe will most likely clear your conscience, such as making up ten days if you are unsure whether it was nine or ten.