Assuming you are asking for AIIMS, then kindly wait for 24 hours and check application status again. Then try to login again for the same reference ID and reattempt payment.
Don't worry, due to excess traffic on the AIIMS website, it is facing some glitches. If your issue isn't resolved in a day or two, then you may fill the application form again to generate a new reference ID.
Good Luck!!!
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