User Management in Self Serve Products

Hey all

What enterprise products does your organization use? Especially those with a self serve payment and then sales/ customer success touch as you upgrade to higher tiers (e.g., JIRA)

Which ones do you like/ dislike and why?

Also, how does the user registration and management work on such products.

I'm working on a product which has enterprise customers with a self-serve model. We are starting to build a User Management and Payments module. If anyone has experience with such products, could you please share how these products usually work?