Despite keeping enough Amazon pay balance, COD order delivered

The domain investor always prefers to use Amazon pay , because it is difficult to find change of 10 paisa or 50 paisa depending on the order amount to pay the delivery person. It is also easier to track the online transactions.
It appears that Amazon is very rigid in processing the subscribe and save orders , approximately 7 days before the scheduled delivery date.
If the balance is not available, the order is immediately converted into a COD, cash on delivery order
However the customer does not get any notification that the order is converted into a COD order.
Only when the delivery person is asking for cash, does the customer realize that the order is converted into COD order.
This can lead to arguments with the delivery person, why the order is converted into COD, despite having an amazon pay balance.

Amazon subscribe and save prices are changing

It appears that the prices indicated in Amazon subscribe and save are changing over a period of time.
For example in September 2018, the domain investor found that the amount payable was Rs 410+ so she added the required amount.
However after a few days she got the notification that she still had to pay rs 12 for the order
That day, the domain investor had some other urgent work, so she could not immediately add funds
She added funds the next day, however the order was already processed and the account was not debited for a particular item

Some Webhosting companies have stopped using WHMCS

One of the consequences of google’s destroying competition, especially link sellers like th domain investor owning this website, is that the demand for webhosting has greatly reduced in the last few years
Google has become extremely efficient at tracking link buyers and penalizing them to increase the Google adwords profits, so very few are purchasing links for advertising.
With fewer customers for webhosting, webhosting companies are forced to reduce their webhosting expenses to the extent possible.
Earlier almost everyone was using WHMCS since link sellers could afford to pay more for webhosting, now most link sellers are broke or have diversified into other fields