Does swallowing something that came out of the nose and was then returned to the mouth during the daytime in Ramadan out of ignorance invalidate the fast, and is it obligatory to make up the days when this occurred?

You must avoid this inappropriate habit. If you expel what comes out of your nose without swallowing it, then your fast is valid and no make-up fast is required of you. However, if you swallowed it intentionally, being ignorant that it invalidates the fast, then your fast is valid according to some scholars. But it is safer and more cautious to make up the fast to avoid disagreement. In the case of making up the fast, if you do not know the exact number of days for which your fast was invalidated, then continue making up the fast until you are reasonably certain that you have fulfilled your obligation, knowing that the basic principle is to take the lesser amount when in doubt, but it is more cautious to make up the day that is doubtful.