# Enroll customer in loyalty program

Enrolls a customer into the loyalty program for a specific shop.

What this endpoint does:
- Activates loyalty features for the customer
- Allows the customer to start earning and redeeming points
- Creates necessary customer records in the loyalty system
- May trigger welcome rewards if configured

When to use this:
- After a new customer signs up on your store
- When enabling loyalty for existing customers
- During bulk customer migrations

Important notes:
- Customer must exist in Shopify before enrollment
- If customer is already enrolled, returns success without error
- Idempotent operation - safe to call multiple times
- Customer ID must be the Shopify customer ID (numeric)

Authentication:
Requires X-API-Key header. Get your API key from the Loyalty app settings in your Shopify admin.

Endpoint: POST /api/external/enroll-customer

## Header parameters:

  - `X-API-Key` (string, required)
    API key for authentication

## Query parameters:

  - `customer_id` (integer, required)
    Shopify customer ID to enroll in loyalty program