How to make a state diagram in "Mobile Payment"?

Question

Software testing

Good evening. The task is to build a state diagram for the function "Payment for mobile communications" in a mobile bank.
It seems that I studied the theory, there is a good article on the same hub, but I’m puffing up. And somehow I don’t even know how to approach this little thing, where to start designing this diagram

Answer 1

Let's start by defining what "state" is in the UML. To describe a state, an Object is required that these states will have.
For example, there is a function (procedure) for agreeing on a Document. The document in the process of approval goes through several logical stages: Development-Control-Approval-Archive. At each of these stages (read each stage is an activity or an action), the document has a number of available operations and properties for working with it, i.e. this series will be a characteristic of the state of the Document object. In this case, these logical stages can be identified with the state of the Document object.
Secondly, you should make an activity diagram and divide it into semantic stages / sections, each of these stages is called a certain state of the object. In your case, this object/entity can be, for example, a subscriber's personal account with the states Positive, Negative, Blocked, Requires replenishment, etc., etc.

Answer 2

I'll add a little.
After the above steps, it's a good idea to define state transitions:
1) What user or system actions lead to the state change? (for example, Positive account -> withdraw amount N -> Requires replenishment)
2) Are there any actions that will not lead to a change in status? (Positive account -> add money to the account -> Positive account)
The result should be a scheme with arrows, and some of them will lead from one state to another (sometimes in both directions - different actions lead to different transitions), and some lead to the same state (but they will also need to be checked, so it is important not to forget about them).