@startuml getBalance
    actor User
    User -> "backend" : getBalance(user_id, token)
     "backend" -> "backend" : confirm JWT token
    alt (token is invalid)
    "backend" -> User : Unauthorized
    else (token is valid)
    "backend" -> "MySQL" : getBalance(user_id)
    "MySQL" -> "backend" : return balance
    "backend" -> User : return balance
    end
@enduml
