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

{
  "payment_method": {
    "payment_method_id": "<string>",
    "billing_details": {
      "email": 123,
      "address": {
        "line1": "<string>",
        "line2": "<string>",
        "city": "<string>",
        "state": "<string>",
        "postal_code": "<string>",
        "country": "<string>"
      },
      "name": "<string>",
      "phone": "<string>"
    },
    "customer": {
      "customer_id": "fcus_01HACM7FZ1084XB1GB6053VM0D",
      "first_name": "John",
      "last_name": "Doe",
      "email": "[email protected]",
      "created_at": "<string>",
      "test_mode": true,
      "phone": "+15555555555",
      "employer": "Flex",
      "shipping": {
        "shipping_address_id": "<string>",
        "line1": "<string>",
        "line2": "<string>",
        "city": "<string>",
        "state": "<string>",
        "postal_code": "<string>",
        "country": "<string>"
      },
      "metadata": {}
    },
    "card": {
      "brand": "american_express",
      "country": "<string>",
      "exp_month": 123,
      "exp_year": 123,
      "last4": "<string>"
    },
    "created_at": "<string>",
    "test_mode": true,
    "off_session": true,
    "metadata": {}
  }
}