Is it obligatory to correct the Imam if he mispronounces the letter "ẓāʾ" instead of "ḍād" in Sūrat al-Fātiḥah in His saying: (Ghayer al-maghḍūbi ʿalayhim wa lā aḍ-ḍāllīn), and does my prayer become invalid by that?

The worshipper should pronounce the Arabic letters ḍād (ض) and ẓāʾ (ظ) from their correct articulation points. However, if they are unable to distinguish between them, their prayer is valid according to the most preponderant opinion. There is no need for them to correct this during the prayer, due to the closeness of their articulation points and the difficulty in differentiating between them. Replacing ḍād with ẓāʾ is excused, and the imamate of one who does so is valid for those who do not, especially for the common people, due to the difficulty of distinguishing between them.