How to receive remote notification with image?

I'm developing an app that uses remote notifications for iOS / Android.
I implemented push notifications using the Firebase Unity SDK.
However, when I send the image it appears on Android but not on iOS.
According to the URL below, for iOS, I have to modify the native source.
https://firebase.google.com/docs/cloud-messaging/ios/send-image
How can I fix it in Unity?
Or is there a way other than the above to send remote notifications with images?

 

Good question!