Dear Tripathi, there have been reports that there are issues regarding payments in the AIIMS MBBS final registration process. Few students tries clearing the cache, browsing history, restarted their device and relogged in. It worked for them. You might as well give it a try. But before that please check if the payment has been debited from your account. If yes  though late you will still be able to complete the registration process. If not, make another payment and proceed further. We understand how frustrating it is. As and when we have an update, we will keep you posted.