Prepaid balance feature

[StellarGuardian]

Is your feature request related to a problem? Please describe.
Currently, this app is very helpful for tracking and reminding future unpaid expenses. However, I have certain expense types that require pre-loading a specific amount of money, which is then deduct periodically (e.g. mobile credit, subscription wallets). I wish I could use the app to track these recurring payments while also being able to monitor and receive alerts about the remaining balance of such funds. Therefore I'd like to suggest a prepaid balance feature.

Describe the solution you'd like
It may include the following elements:

1. A new optional "Prepaid Balance (or other suitable names)" numeric field in the expense editing page.
   If set, the current balance will be displayed on this item in Home tab; and the Upcoming Payments tab shows the projected balance after each future payment.

2. On each payment date, the app will deduct the item's Price from its Prepaid Balance; the value in the Home tab updates accordingly.

3. A new switch for low-balance reminder. If enabled, when a deduction leaves a balance insufficient for the next scheduled payment, the app will send a warning notification.

Use Case Example:
User sets a $95 prepaid balance for a expense item with Price of $10/month.
After the first month's payment, the balance drops to $85; the second month, drops to $75...
After the 9th payment, balance drops to $5, less than the requirement for the 10th payment. The app then sends a low-balance reminder, so user remembers to top up enough before the 10th payment occurs and edit the balance value within the app.

4. Regarding the Totals info in the Home tab and Upcoming Payments tab, although the actual payment has already been made for these prepaid expenses, but from the perspective of reflecting the total value of all recurring financial commitments being consumed within a period, I think it's appropriate to include them in the statistics as usual.

Some of other potential features might help provide finer control, such as the ability to pause the expense when the balance is insufficient (#475), or a switch to exclude them from the statistics (#695).

With the above features currently not available, to maintain the app's simplicity, I think it's fine to have the prepaid expenses just work the same way as other regular expenses and keep them active in statistics (regardless of whether the balance is sufficient, insufficient or negative), except they have an additional balance value to be tracked. If the expense ceases, users can manually delete the item to stop it from appearing in statistics. But I'd love yo hear your thoughts if there's any flaws or other better approaches.

Thank you for taking the time to read this!

Describe alternatives you've considered, if any

Additional context

[DennisBauer]

@StellarGuardian thanks for the feature request. I do agree this is a valid use case, even though it is probably a niche one. For the upcoming payment screen this will definitely need to be visible there. With a 0 payment for the current recurrence while still showing the normal price and probably also the remaining balance.