Service Blueprint | Align support service with Backstage Interaction

I'm learning how to build useful service blueprints, and I find it hard to understand the difference / relationship between backstage interactions and support services. I'll show you a part of my setup.

Physical evidence
Login screen of the smartphone application
user action
Complete the registration form
Interaction in front of the stage
Registration form, Send button, remember username
Interaction behind the stage
??
Support services
PhP / MySQL user authentication implementation

What is the back of the stage interaction in this situation? Is it "application communicates with database"?

I'm trying to understand the framework of this framework and I want to make sure that I understand the proper way to implement it. Let me add another example so that I can report my use of faux pixen.

Physical evidence
Smartphone application settings screen
user action
change settings
Interaction in front of the stage
User settings form, Submit button
Interaction behind the stage
Application communicates with the database
Support services
PhP / MySQL implementation for storing user settings data