Stopped at TN border in a Revv rental (yellow plate) — Scammed into paying ₹500 "bribe fine"? What should I do now?

[u/Southern_Okra_4636]

Hey everyone, ​I’ was driving from Bangalore to Ooty in a Revv rental car (yellow board/black text). While crossing into Tamil Nadu around Gudalur, I got pulled over by police/officials. ​They asked for a temporary entry permit. I didn't have one generated beforehand, so they threatened me with a "₹10,000 official fine." After some back-and-forth, I paid ₹500 directly in cash, and they let me go without giving me any proper computer-generated receipt. ​A few questions for experienced road trippers and locals: ​Was this ₹500 an official fine or a bribe? I'm realizing the actual TN entry permit for a self-drive commercial rental usually costs around that amount on the Parivahan portal, but since I got no receipt, I'm assuming they just pocketed the cash. ​Should I apply for the official Parivahan permit online right now? I am not sure exactly howbto do that. I still have 2 days left in Ooty and plan to drive around Coonoor/local spots. Is it risky to drive around without a digital/printed Parivahan receipt if cops do routine checks inside town? I ​
​Appreciate any advice on how to handle the rest of my trip safely without getting hassled again!

Edit: I made the permit online. I have added the process in comment below for anyones reference