The two Kingdoms gave a pretty straight-forward response to the envoys, and that was direct beheading of the envoys, and everyone following them.
Even in war, the envoys weren't supposed to be harmed, as it would make it impossible for Kingdoms to ever trust each other again in the future.
Killing the envoys meant that both countries had decided to either come out victorious and become the rulers of the Lava Layer, or perish in the upcoming war.
Of course, one had to understand that these two kingdoms currently had the upper hand, as not only hadn't they suffered any damage until now, but they were even cooperating together.
The Moth Kingdom was the one to think of this attitude the worst, as they felt like they had been too peaceful before and now they were being thought lowly.
Unfortunately, no matter how much they wanted to give a strong response to the enemy they didn't dare.