How to do chatting in two apps

I have two apps for the client and serviceman so I want to do add a screen for chatting . But the problem is there are two apps and I only know the coding of making chatting possible in only one app the receiver and the sender are both in one app. but here the sender and the receiver are v in two apps one for the sender and one for the receiver so please help me.:relaxed::relaxed::relaxed::relaxed:

If you can do this

Then you can easily do this also

You can use firebase to store the massages and show to the receiver

create a app use firebase or other data to store and show msg.
in this send and receiver are same database connected so there is no problem.

This one can be help to you: