The correct reading is みすい. 未 (み) and 遂 (すい) both use their standard On'yomi. Misreadings like みえい misidentify 遂. 未遂 refers to an attempt that was not successful or accomplished, particularly in the context of a crime, describing something intended but not completed.

正しい読みは「みすい」です。未(み)と遂(すい)の音読みです。「みえい」は遂の誤読です。未遂は、何かを試みたものの、最終的な成功や達成に至らなかったこと、特に犯罪の文脈で使われます。