Yes, the ability to add late fee for past due invoices automatically, with simple options like1. A fixed amount and 2. a % of the overdue amount and a minimum amount
It is so much work to do this manually!

I feel like a lot of people ask for this and it's super important to ensure fast collections. For reference, I can provide our specific terms of service (which are fairly standard):

If we do not receive payment of an amount due on your account by the specified required payment date, it will be subject to a late payment charge of 3% per month. This late payment charge will accrue on a daily basis and will be calculated and compounded monthly on the outstanding amount (42.58% per year) from the date of the first bill on which it appears until the date we receive that amount in full.

This is a common ask across zoho finance in several areas. You guys might want to merge ideas together. We have late fees built into our agreements but very rarely actually act on them because Zoho won't automatically add them on. In our case due to running in accrual accounting and the integration with avalara we would need this to be more of an interest invoice generator for past due balances that automatically invoiced the client some % of their balances with detail.

Could be like Invoice XXXXX Original Amount $xxx.xx Amount Outstanding $xx.xx Interest Rate 18% APR = $xx.xx interest per day then enter the number of days overdue in the qty and the rate per day in the rate field. This would have to run down per invoice and these invoices would have to run on a specific day each month or something.

This is just one idea. I know running these types of things can become complicated which I am sure is why this isn't implemented.