Praise kink

The submissive partner gets off on being praised and “earning” approval. The dominant showers them with “good girl/boy,”“you’re doing so well,”“I’m so proud of you” whenever they please them. The sub might perform acts just to hear that praise. You can gamify it (each time they do something particularly well, you verbally reward and maybe give a physical treat like a kiss or a few seconds of vibrator).