yes, I am very sure it is created by BuddyPress. It only appeared right after I’ve done those mentioned (installed, deactivated, and then tried to remove BuddyPress’s all files). I didn’t install any plugin during this period.
That’s what I did, but it is still showing the error “Vendor registration is currently closed. if you have an existing account, you may log in and apply to become a vendor”. How do I fix this? I think the code is not completely removed from WordPress even when I delete BuddyPress in Plugins.