From Concentrate

When a creature takes this feat, they gain the ability to cast two spells that require concentration at the same time. In order to do this, both spells have a half duration. Bonuses of the same type do not stack. A creature casting two spells that require concentration may not use reactions. At the end of the creature's turn, they must make a concentration check DC 10 to maintain focus on the second spell. If the creature is damaged, they must make two concentration checks. If the first fails, the concentration for the first spell is lost. If the second fails, concentration on the second spell is lost. If both fail, concentration on both spells is lost.