curl --request POST \
  --url https://api-v2.missioninbox.com/billing/create_subscription/ \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '{
  "price_id": "<string>",
  "payment_method_id": "<string>",
  "coupon_code": "<string>"
}'

{
  "subscription_id": "<string>",
  "status": "<string>",
  "current_period_end": 123
}