Does reading "أنعمتا" with madd on the tāʾ, or "أنعمتا عليهم" in Al-Fatiha, constitute a subtle melodic error (taḥlīn khafī) or invalidate the prayer?

Adding an alif after the taa’ in the word (an'amta) in Surat Al-Fatihah is a لحن (mistake in recitation) that does not invalidate the prayer because it does not change the meaning. However, the person who recites it this way should be advised and alerted, while exercising wisdom and gentleness, because it is not permissible to intentionally recite it in that manner.