You can promote your content from your Organic Public Story, Saved Story, or Spotlight content with ads on mobile, directly in the app.
To be able to promote content in-app, you must have a role on the Profile and be either an Account Admin, Campaign Manager, or Organisation/Business Admin on the connected ad account. You can learn more about roles and permissions here.
Go here to learn how to promote a Snap In-App on iOS.
Take advantage of all Snapchat has to offer. Promote your Snap to get more views and followers. Learn how to get started with Snap Promote.