My client and I agreed on an architectural design for an android application, which included the MySQL database. The application has been released, and has grossed a good number of users and data. The client is suddenly asking me to modify the back-end and use Firebase instead of MySQL because he talked to someone from Google who suggested Firebase would be better.
The client has a notion that integrating Firebase is a very simple task. How can I make the client understand that completely changing the back-end is not a minor enhancement or bug fix, and that this will take some time to implement and incur an extra cost? I'd like to politely explain these facts as there is a string chance of me securing another project from them which I am particularly interested in doing. Please offer your suggestions.