Dear Shagun, there have been reports regarding the payment for Final Registration process. AIIMS hasnt officially announced any solution for this. But few students who have actually faced the same issue, cleared the cache, browsing history, etc, restarted their devices and relogged in. It worked for few. You might give it a try as well. It might work or might not work at the very first instance but eventually you will be able to complete the final registration process. Just don't panic and give up yet.