What is the ruling regarding the prayer of the Imam and those praying behind him if they differ in determining the Qiblah, with each believing their determination to be correct?

If the Imam and the congregants differ significantly on the direction of the Qibla, such that each party believes the other is mistaken, then the congregants are not permitted to follow the Imam. This is because each of them is a mujtahid (one who exercises independent reasoning) who sees the other's mistake. However, if the difference is minor, such that they agree on the general direction but differ on inclining slightly to the right or left, then following the Imam is permissible. This is because the condition is facing the direction, which has been met. It is assumed that differences among mosques would be minor, as the mihrab (prayer niche) faces the Qibla. And it is obligatory for whoever does not see the Kaaba to exercise ijtihad in determining the Qibla.