> ## Documentation Index
> Fetch the complete documentation index at: https://billing-docs.razi.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Authentication and Plans

> Learn how to authenticate and retrieve billing plans

<Warning>
  The below authentication in all the flows related to the billing API is handled by the client backend app in same way above.
</Warning>

This guide explains the flow for authentication and retrieving billing plans using the Billing SDK.

## Get Plans Flow

<img src="https://mintlify.s3-us-west-1.amazonaws.com/locai-6a77a221/images/Billing-Setup.png" alt="Billing Setup Flow" />

<Tip>
  You can use the <Link href="/sdk/hooks/usebillingplans">useBillingPlans</Link> hook to retrieve the plans and entitlements.
</Tip>

<Steps>
  <Step title="Client UI Initiates Request">
    The client UI calls the `useBillingPlans` hook to trigger a call to the billing API.
  </Step>

  <Step title="Billing API Validates Session">
    The billing API queries the client backend app to check the validity of the session and retrieve user details.
  </Step>

  <Step title="Return error to client if session is not valid">
    If the session is not valid, the billing API will return an error to the client UI.
  </Step>

  <Step title="Billing API Queries Lago">
    If session is valid then based on the user details, the billing API queries Lago to return the plans for the user. Currently, all plans are fixed for each client.
  </Step>

  <Step title="Lago Returns Plans">
    Lago returns the relevant plans to the billing API.
  </Step>

  <Step title="Billing API Responds to Client">
    The billing API forwards the plans back to the client UI. The `useBillingPlans` hook receives the response, which includes the plans and any potential errors.
  </Step>
</Steps>

<Tip>
  You can use the <Link href="/sdk/hooks/usebillingplans">useBillingPlans</Link> hook to retrieve the plans and entitlements.
</Tip>