וַיָּק֙וּמוּ֙ שָׂרֵ֣י מוֹאָ֔ב וַיָּבֹ֖אוּ אֶל־בָּלָ֑ק וַיֹּ֣אמְר֔וּ מֵאֵ֥ן בִּלְעָ֖ם הֲלֹ֥ךְ עִמָּֽנוּ׃
And the princes of Moab rose up, and they went unto Balak, and said: ‘Balaam refuseth to come with us.’
Or HaChaim on Numbers
מאן בלעם הלך עמנו, "Bileam refused to come with us." They suspected him of being a liar, accusing him of desiring more honour than what Balak had shown him thus far. It is also possible that seeing that Bileam had promised to inform the emissaries immediately of G'd's answer but had not done so until morning, this made them assume that he told them what he wanted them to know and not what G'd had told him. Perhaps there was even a traditon that Bileam was a compulsive liar.
Rashbam on Numbers
הלוך עמנו, for we do not appear as men of substance in his eyes.