Answer
High temperature.
Work Step by Step
Given that the reaction is endothermic.
That is, $\Delta H\gt0$.
Since the number of moles of gas increases from 2 to 3, the entropy increases and $\Delta S$ is positive.
$\Delta G=\Delta H-T\Delta S $ is negative for a spontaneous process.
Since $\Delta H$ and $\Delta S$ are positive, $\Delta H-T\Delta S\lt0 $ only at high temperatures.
