Is it obligatory to do something as an expiation or the like for violating the website's terms by teaching some students outside of it, after their request to leave was refused?

The website stipulated that the teacher should not agree to teach students outside the platform, and this condition must be fulfilled, based on Allah's saying: "O you who have believed, fulfill [all] contracts," and the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions." As for students who left and do not wish to return, the teacher must either refrain from teaching them outside the platform, or seek permission from the website administration. If they grant permission, then [it is permissible], otherwise, he must refrain.