In order to work at the celestial palace, he went to the Angel trials and got sent in the devildom

It's simple really. All he has to do there is survive for a day without getting tempted by demons.

Spending his time in a casino, you were flirting with him to get him to gamble and despite that he was all blushy he was denying it

"I- I can't do that ya know?! I'm an angel!" He said shaking his head