What classifies an app as a Sticker app?

Hi,

I have an app with an accompanying iMessage extension that lets users send stickers. The iMessage extension however is not included in the iMessage 'Stickers' list but instead in the 'More' section despite the fact that it is used to send stickers. (iOS 17+)

I also cannot select 'Sticker' as a category for my app (even after uploading the build).

Is there any way for me to classify my app's iMessage extension as a Sticker? Would appreciate any help and thank you!