Korean · Pronunciation Guide
ma-ni. The ㅎ inside the cluster ㄶ is deleted outright before the vowel, so there is no h in this word at all.
mani
Two blocks, both short. The rule on show is ㅎ-deletion: the same cluster that aspirates a following stop in 많다 simply loses its ㅎ before a vowel, so this word and 많다 sound far less alike than their spellings suggest.
Listen: 많이
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오늘 많이 걸었어요.
Oneul mani georeosseoyo.
I walked a lot today.
Listen: 오늘 많이 걸었어요.
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오늘 많이 걸었어요 puts the adverb in front of a past-tense verb, and 걸었어요 chains two resyllabifications, giving geo-reo-sseo-yo with a tap and then a double s. Nothing in the whole sentence has an audible h in it.
Trying to pronounce the ㅎ gives 'manh-i' or 'man-hi', and neither exists -- before a vowel it is simply gone. The other error is failing to move the ㄴ across, producing 'man-i' with a syllable break, when Korean carries the consonant forward and the word is two smooth beats with no seam.