Creates a new expense in Expensify.
- Merchant (text): The company the expense was paid to.
- Expense Date (text): Date in format YYYY-MM-DD.
- Amount (number): The amount of the expense.
- Currency (text): The ISO code for the currency.
- External ID _(_number): Should be unique.
- Category (text): Entertainment, Fuel/Milage, Lodging, Meals, Other, Phone, Transportation
- Tag (text): Add an optional tag.
- Billable? (T/F): If it is billable.
- Reimbursable? (T/F): If it is reimbursable.
- Comment (text): Additional information.
- Transaction ID (text): The ID for the expense.
- Created At (text): When it was created.
- Merchant (text): Where the money was spent.
- Amount (number): How much was spent.
- Currency (text): Which currency (ISO, see above).