List Customers

curl --request GET \
  --url https://api.withflex.com/v1/customers \
  --header 'Authorization: Bearer <token>'

{
  "customers": [
    {
      "customer_id": "fcus_01HACM7FZ1084XB1GB6053VM0D",
      "first_name": "John",
      "last_name": "Doe",
      "email": "joh.doe@example.com",
      "phone": "+15555555555",
      "employer": "Flex",
      "shipping": {
        "shipping_address_id": "<string>",
        "line1": "<string>",
        "line2": "<string>",
        "city": "<string>",
        "state": "<string>",
        "postal_code": "<string>",
        "country": "<string>"
      },
      "created_at": "<string>",
      "test_mode": true
    }
  ]
}