License and download a Shutterstock image with a specific size/format, tracking subscription quota via the subscriptions endpoint

Steps

1. Obtain an OAuth Bearer token with licenses.create, licenses.view, and purchases.view scopes
2. Call GET /v2/user/subscriptions to see which subscription_id(s) are available and which formats/sizes each permits
3. Call GET /v2/images/{id}?view=full to confirm the desired size/format is licensable (is_licensable: true) before licensing it
4. License the asset with POST /v2/images/licenses, sending an images array with image_id, subscription_id, optional format/size, and (for API subscriptions) required price and metadata.customer_id fields
5. Retrieve the file using the download.url returned in the response, noting it is only valid for 8 hours
6. If a fresh download link is needed later and the license type permits it, request one via POST /v2/images/licenses/{license_id}/downloads instead of re-licensing