Push usually triggers synchronization
Clients register and refresh device tokens, and unregister when appropriate. Push types and encrypted payloads have distinct rules. Receiving a system notification does not establish complete message state or user reading.
Acknowledgments have different meanings
A quick acknowledgment is not the final business response. After interruption, reconcile message identifiers and differences rather than repeatedly sending the same content. File transfer may use appropriate separate connections.
Product recommendations
Associate refreshed tokens with the correct account and device, and revoke obsolete bindings on logout. Limit push payloads to necessary identifiers. Recover conversation state from a trusted source when foregrounding, reconnecting or opening a notification.
Test foreground, background, locked-device and system-restricted conditions separately. Track request submission, provider acceptance, device receipt and notification opening as different metrics; one successful delivery does not guarantee every device state.