With the booming development of the network economy, B2B e-commerce platform companies generally adopt the freemium business model, accumulating the amount of platform users through free strategies and promoting seller users to pay with the help of network effects. Despite the proliferation of studies on the network effects of platform marketplaces, it remains unknown whether the presence of free users will promote or discourage seller users from paying. From the perspective of dynamic management of free user engagement differences, this study explores the dynamic impact of the increase in free users with different engagement levels （ad-led traffic users and registered resident users) on the payment behavior of platform sellers’ users in the context of B2B e-commerce platforms. This research uses the VAR model to analyze 366 days of data from a B2B e-commerce platform and finds that search ad-led users are more likely to motivate the participation of seller users and boost the number of resident sellers; while social media ad-led users are more likely to facilitate the participation of buyer users and boost the number of resident buyers; but in both the short and long term, the number of resident sellers is more likely to boost the willingness of platform sellers to pay than the number of resident buyers.