Login/Signin API need modify to taken and store user Push token.
Need API to set state of User: When the app is not on focus, then it will set user state to accept.
push notification (otherwise user will receive Push notification even when they are chatting).
Need new API to return number of unseen message.
Need new API mark conversation is Read and reset unseen number.
Above is first task.
it will be more - ongoing position. It depends on yourself absolutely.