Flutter and RealtimeDatabase - Option for Point Of Sales Hybrid Cloud?

Hello everyone.

We have just finished our ASP.NET Core Web App ( An ERP for businesses in the food industry )

The ERP will be hosted on a VPS and lets each client manage their Sales, People,…

Now our next step is to develop a Point of Sales system for these clients, which they will use in their Stores.

What drew me to Flutter is the Cross-Platform benefits in brings and also that we are looking for some kind of Hybrid Cloud, where we could use Flutter and maybe Hive to do our ‘offline sales’ and then synchronise this with the VPS ERP Application.

I drew a little map to show visualize what I am talking about

The circle will be where the VPS is and where data would need to be synchronized to.
The orange box is where the synchronization will happen for that specific Store.
The black squares indicate Clients, or maybe Stores from Clients. In this case, I drew two seperate Clients.

Each Green box is a Point of Sales where our new application will run on.
They would be connected to the orange box so that one employee can jump from one Point Of Sales to another and so that they can all get an update on for example, new Products, or maybe Orders from clients via the ERP. I think you know what I mean, they have to be aware of the same data that they process, but this does not go to the VPS, only certain data will be synchronized (actual sales, … )

I also wonder how good the support is to connect external devices (like Native would, Bluetooth, Scales, payment machines,… )

I am wondering if anyone could give me some tips / advice / resources to help me accomplish this rather complex issue.

Kind regards,
Jara