Looking for correct registration hook

I am working with the developers of the Universal Profiles Made Easy plugin (UPME) to auto approve new user profiles for users who have registered via s2member. In order to do this I need to execute some custom code just after the registration is completed and a new user is created. My question is what action gets executed just after completing registration? I need to be able to submit the user ID as a parameter to the profile plugin. Looking at the registration hook list (https://www.s2member.com/codex/stable/s2member/registrations/package-filters/) I am not sure which one would do that.

https://www.ads-software.com/plugins/s2member/