Taking a step back, what I'm trying to say is at the very least the SuiteTax part of india localization is not functional. It is a broken buggy mess.
Not too familiar with NetSuite legacy tax and India localization though, maybe that's better, but until 2021.1 you won't be able to have tax compliant sequential numbering as for as I know. A while back we had to see if the India GST can be a customizable scripted solution, I can't remember correctly, but it was along the lines of some duty on top of a tax rate and some calculation was involved to break it into lines. Not sure if the India tax landscape has changed since then though!
I'm not a tax accountant, but in the end, our client didn't go through it as a scripted solution, I was off this project, so I'm not sure what my colleague did!
Another client of ours is using SuiteTax plus india localization though, but I highly recommend NOT using it. It's really, extremely broken.