PratikArora I was not even able to regenerate the issue successfully.
I setup a new staging server, created new api keys and webhooks and did everything.
Then for the first two payments I got an issue. Glad I was logging the API response on the server.
I found that the Razorpay API sent a response that was creating the order on Razorpay was sending the response as "Currency not supported" but the "INR" currency was being sent properly.
After a couple of minutes, I tried to place an order again and it worked without any issue.
I created about 30-40 orders after that just to recreate the issue again, but that issue never occurred again.
I guess, there could be some issue with Razorpay API that their API was not able to parse the currency properly. (I googled this and found some other users faced this issue too, but no resolution)
Marking this as an exception.
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Regarding the order notification thing, I will check that and update accordingly.