The deal is said to have earned her between Sh6 million and Sh8 million.
Joey is said to have handed in her resignation letter on Wednesday after she discovered that disciplinary action was coming her way.
A source who spoke to Pulselive.co.ke on condition of anonymity, revealed that Royal Media Services (RMS) took issue with their 'Power Breakfast' anchor for allegedly working for their competitor.
Conflict of Interest
RMS is the parent company to betting site Shabiki.com and it is their alleged considered opinion that Muthengi should not work for their rivals.
"The deal she was given brought a conflict of interest and to avoid a nasty exchange with her employer she opted to leave.
"Since Shabiki is owned by RMS, I think there was a problem because she was earning between Sh6 million to Sh8 million from Betin," the source revealed.
Credible reports further add that Joey is scheduled to travel to Italy alongside her Betin co-ambassador McDonald Mariga to shoot more adverts for the betting company.
The two have featured prominently in Betin's media campaigns as they play the roles of husband and wife in the popular adverts.
Mariga signed an year-long deal with the company that earned him Sh8 million while Joey was previously rumoured to be taking home a six-figure cash out from the advertising deal.