What should one do who, out of ignorance, prayed the Maghrib prayer as two rak'ahs while traveling, and what are the consequences if he similarly issued a fatwa to someone else?

Whoever prays Maghrib two rak'ahs out of forgetfulness or ignorance, their prayer is invalid and they must repeat it, because they omitted an entire rak'ah. Travel does not affect the Maghrib prayer. Whoever does not know the number of invalid prayers should pray what absolves their responsibility. It is obligatory to inform those who were misguided into shortening the Maghrib prayer that their prayers are invalid. Likewise, it is obligatory for every accountable individual to learn what is an individual obligation (fard al-ayn), such as prayer, and not to speak about Allah without knowledge.