Is it obligatory to repeat a word in prayer if the pronunciation of the letter Sīn (س) or Ṣād (ص) is somewhere in between, given the proximity of their points of articulation?

If a letter comes between the letters Sad and Seen, then if he is unable to learn, his prayer is valid. But if he is able, it is obligatory for him to learn, and to make up the prayers he missed due to his negligence in learning. We advise you to turn away from whisperings (waswas) and not to pay attention to them, and not to repeat the word about which you have doubts.