curl --request POST \
  --url https://api.withflex.com/v1/setup_intents \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "setup_intent": {
    "partner_id": "<string>",
    "checkout_session": "<string>"
  }
}'

{
  "setup_intent": {
    "setup_intent_id": "<string>",
    "client_secret": "<string>",
    "customer": {
      "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>"
      },
      "metadata": {},
      "created_at": "<string>",
      "test_mode": true
    },
    "description": "<string>",
    "payment_method": "<string>",
    "partner_id": "<string>",
    "metadata": {},
    "created_at": "<string>",
    "test_mode": true,
    "status": "requires_payment_method",
    "usage": "off_session"
  }
}