How do i find the following API details: Login API, Signup API,Subscription Details API, User Details API

Question:
Where can I find the following documentation? Login API, Signup API,Subscription Details API, User Details API.

Product:
Wix Studio Editor but not a responsive template.

What are you trying to achieve:
I am building a user app for my members to go along with the site. The items the app developer is requesting is to sync the members and payment plans with the website so if someone uses an email to make an account on our site and buys a membership, that same membership and account will be linked to them when they log onto the app as well.

What have you already tried:
From what I have found online, I go to the CMS on the websites dashboard in the wix studio and then go to Wix App Collections but from there I’m lost on the next steps.

Additional information:
I am not looking to make an app through wix but a fully native ios app. Im not looking to use Wix Blocks or anything like that.

For that, your app developer will need to go through Wix Velo docs, where they will find all the necessary info:

I’ll list the specific APIs that your dev might need:

wix-members for fetching user details, along with handling signup and login.
wix-pricing-plans for fetching details about your site’s payment plans.

Your dev might need to export all this info using an API endpoint for your website, for which they can use http-functions.