Best practices
Prefer providing one primary experience in your iMessage app.
Consider surfacing content from your iOS or iPadOS app.
Present essential features in the compact view.
In general, let people edit text only in the expanded view.
Create stickers that are expressive, inclusive, and versatile.
For each sticker, provide a localized alternative description.
For the complete guidance, including worked examples and illustrations, see the canonical page: https://developer.apple.com/design/human-interface-guidelines/imessage-apps-and-stickers