Ahem. This is an interesting topic to come about since I remember this quite well, having been brief King of the Dominion of Alluran at the very outbreak of the Invasion and then the person who started negotiating with the monsters.
Enweil sold us out to the monsters. Quite explicitly so. The monsters had a really interesting RP atmosphere going on about trying to stop the daimons destroying everything whilst still being quite savage themselves. When I allied the remnants of the Dominion with them Enweil went all out on calling us out on it, despite having had their own deals from what I could find out. Then they sided with the daimons.
That's an instance of more... blatant lying.
It's not lying.
What was happening was that Mordred of Riombara was having discussions with the monsters, without authorization if I recall (but he was judge), to side with the monsters against Enweil. Guillaume knew this, so he also approached the monsters. Enweil offered them some food as gifts, and when asked for a good place to settle, Guillaume told them about how nice and lush the Eno delta was. After a close call (they almost sided with Mordred), there they went. And there they pursued their agenda. Almost immediately, they attacked Enweil to "test" us. We kicked their asses. They didn't like that too much. Things escalated. The alliance with the daimons only came after a serious beating from the monsters, when it was clear we couldn't keep up.
There was no "deal" with the monsters. We sent them bribes and incited that they attack DoA instead of Enweil, but no "deal". The monsters never offered or promised anything to Enweil. We didn't want any invaders, neither with nor against us. But when things started getting heated, it seemed much more reasonnable to call in the daimons so that inhumans killed inhumans, instead of having the monsters kill a bunch of human realms down South, and the daimons kill a bunch of human realms up North. Pitting them against each other made the daimons less effective in their efforts to kill other human realms, and slowed the monsters in their own efforts to kill human realms. Net result was less destruction on human realms, even if some (KoA, Avalon) died and others (Enweil) were left as good as dead.