Create App Update Notification Server?

I made an app, but when there is an app update, I put up a pop-up window.

I'm trying to text you to update because there's an update.

So I made a file called update.txt on my server, and on the first line, I wrote a version for version check

In the second line, I want to write a message and check it every time I run the app

But when you implement these functions, you don't do it like this, right?

Do you implement it with restapi, etc Or how do you usually implement it?

Thank you^{^}