Airtel app does allow for prepaid customers to enter their GSTIN, and Jio does/ used to do that as well. I could not try that out with Airtel since while converting post to prepaid they got my address totally wrong, so essentially State Code was not registered in my address and I could not enter my GSTIN. I think Airtel has that infrastructure in place. They will issue invoices with GSTIN of customer even for prepaid, if the customer has entered GSTIN.
I wanted to know, do people feel a difference in network quality between postpaid and prepaid even today?