themes app background not showing up

[JayFME3996]

i downloaded some themes off the galaxy store, everything works from icon to wallpapers except when i opened my phone app and messenger app. it does not have the custom background shown from the theme photos.

[larky]

I think its cause messengers a sep app altogether,it should show wen u messaging in messages 🦋

[JayFME3996]

i meant the default phone and message app sorry, like this one https://www.samsung.com/us/support/answer/ANS00078947/ 
under message customization.

i have samsung ultra 20, current software it say SM-G988B or G900BXXU3ATG4