Hi all, Need some small suggestion. I have an ionic Cordova application

Question

Hi all, Need some small suggestion. I have an ionic Cordova application

with node js and mongo dB as a backend.
I want to implement a simple one-to-one chat feature (patient with doctor and vice-versa).
Which is the best way to implement this?
Using firebase or to use my existing MongoDB and node js.
Please say the pros and cons also