When users click "Add New Expense," they must click "Add New Payment" to enter the payment, and "Add Expense" to save (this is hypothesized as the code doesn't work.) Meanwhile, deleting an expense takes a single button, without any warning prompts.
Introduce autosave, or remove the "Add New Payment" option to at least only require one click to save an expense. Replace "Add New Payment" by always ensuring that at least one row of new expense is shown at any given time. Have users confirm deletions.
The app limits users to edit one expense at a time. This is highly inefficienct and forces users to fill out each form in the order give, even if it may be more efficient to fill out all costs first, for example, if an user was referencing a bank account.
Add in -- potentially as an advanced option -- the option to add multiple expenses and line items at once, without having to trigger more inputs by successive button press.
When the page is refreshed, all previously-added expenses are gone. Since an expense app keeps track of expenses over time, not being able to view past expenses makes the app inefficient to use.
Add in an auto-save option to restore the state of the webpage after exiting.
The fields for Title, Date, and Payment (amount) defaults to empty when an expense is added.
Set defaults for fields that have natural defaults: