How can I update the database information in a installed App when the player pays for an upgrade

The database will be updated when your code updates it. If the database is part of another system you’re using, then figure out how to use that system’s API to update it.

NOTE: almost nobody uses MySQL to store data on the client side. Doing so makes things FAR more complex because there will be hardly any examples or tutorials to draw from.

Yes, you can MySQL, but you will largely be developing everything alone without any help from the internet at large, since nobody does that. Using MySQL at all buys you about 100x the complexity and surface of potential error so I would NEVER recommend it, especially for a beginner.

Otherwise, just save it like any other play data. Here’s more reading:

Load/Save steps:

An excellent discussion of loading/saving in Unity3D by Xarbrough:

And another excellent set of notes and considerations by karliss_coldwild:

Loading/Saving ScriptableObjects by a proxy identifier such as name:

When loading, you can never re-create a MonoBehaviour or ScriptableObject instance directly from JSON. Save data needs to be all entirely plain C# data with no Unity objects in it.

The reason is they are hybrid C# and native engine objects, and when the JSON package calls new to make one, it cannot make the native engine portion of the object, so you end up with a defective “dead” Unity object.

Instead you must first create the MonoBehaviour using AddComponent() on a GameObject instance, or use ScriptableObject.CreateInstance() to make your SO, then use the appropriate JSON “populate object” call to fill in its public fields.

If you want to use PlayerPrefs to save your game, it’s always better to use a JSON-based wrapper such as this one I forked from a fellow named Brett M Johnson on github:

Do not use the binary formatter/serializer: it is insecure, it cannot be made secure, and it makes debugging very difficult, plus it actually will NOT prevent people from modifying your save data on their computers.

A good summary / survey of the problem space: