You need to format your notification payload in a specific format that is not a public API and isn’t documented right now. You don’t need to modify the manifest, but the format is implied by the Expo client source code.
Android: https://github.com/expo/expo/blob/e543a7be75dfa4f6a66a98070e011e17c53f0b5d/android/expoview/src/main/java/host/exp/exponent/notifications/ExponentNotification.java#L29
iOS: expo/EXRemoteNotificationManager.m at d718b4b8c390c116837c4d440c06085cca8db5b0 · expo/expo · GitHub (Same as a regular iOS payload, with a “body” field for arbitrary data. You may need to specify a field named “experienceId” with @yourexpousername/yourprojectslug as well.)