We want to be able to send mobile push notifications to a third-party app on Android and iOS without changing the app in any way (e.g. adding an SDK). Target apps may or may not have FCM SDK installed. We do not have control of the target app. We will be given relevant device IDs etc and granted access by the app owner.
How can this be done? What are the requirements, technical set up etc? Can we use Firebase for this or do we need to integrate directly with the notification servers?
Can we receive read receipts and / or other feedback from the app instances? Again, without touching the target app code
Thanks! Axel