Rui found it truly regrettable that he was unable to hide the fact that he could fix the Martial Prince's problems. But when the cat came out of the bag, he swiftly came to a decision to offer some means of cooperation instead of refusing to cooperate.
This was because he truly did not want to earn the enmity of an entire faction by operating in bad faith.
After all, he had promised that he would do his reasonable best to help the prince. The Martial Prince had acted in good faith this entire time, and it was Rui who went against the spirit of their deal.
Breaking out of their deal with the severance pay would mean breaking ties with the Raijun Faction on bad terms. That was a level of pressure that he could not handle even as a high-grade Martial Senior. Had he been a Martial Master, he would have been able to get away with it, but alas, he was not.