Gamification becomes an important and widely used instrument in online learning, and it affects users' experience. However, recent research on the interaction between a user and technology, in the online learning platform, tends to study gamification separately. This paper aims to overcome the research gap, exploring the relationships between user engagement, platform affordances, and gamification in online learning. An online survey was conducted among the participants (N=375) studying with Skyeng (commercial online platform for learning English). The data was analysed with factor and regression analysis. The results demonstrated four major platform affordances: technology credibility and usability, adaptability of course tasks, phasing and intermittence and external reward. Among the four, technology credibility and usability was found to be the most influential predictor of user engagement in online learning. External reward, as an affordance, drawn from gamification elements, has the smallest contribution to user engagement. However, the study proves the suitability of perceiving gamified elements as affordances by platform users. The research provides conceptual and empirical grounds for studying gamification elements as one of the affordances in online learning and outlines further directions to explore these connections.