Does congregational prayer become invalid if the Imam recites "ولا الضالين" (walad-dallin) by mixing the letter Dhaad with something of the letter Zay instead of pronouncing it correctly?

The most deserving person to lead the prayer is the one who recites the Quran best. If someone mispronounces the letter "ض" (Dhaad) due to its difficulty, for instance, by pronouncing it as "ظ" (Zhaa) or "ز" (Zaay), their prayer is valid, as Allah Almighty says: (Allah does not burden a soul beyond its capacity). Their imamate (leadership in prayer) for others is valid. The error in "ض" (Dhaad) and "ظ" (Zhaa) is overlooked due to the proximity of their articulation points and the difficulty in distinguishing between them, especially for non-Arabs. Therefore, if someone substitutes "ض" (Dhaad) with "ظ" (Zhaa), their prayer is valid.