He works for the CIA and they (the US Government) were trying to buy stolen Vibranium from Klaw. It's why Ross was at the casino.
Our previous encounter had me in his custody after a series of events involving my people, the Avengers, and the U.S. Government. Because of my status (King of Wakanda) and the fact I was not an Avenger, I was eventually let go, but I made a deal with him to keep my identity as the Black Panther a secret. Currently, the world thinks Wakanda is a poor, third world country, when it is anything but. The Black Panther suit would immediately reveal that secret, as it is made of Vibranium, a rare element worth a lot of money.
Ross is trying to act as if that favor holds weight when at the moment I could care less. I promised my people I would bring Klaw home to Wakanda to face justice for what he did.