Dear Mugdha

You need to clarify your question a bit more. 

First of  I need to know which exam application are you talking about- is it NEET 2018 or AIIMS MBBS 2018?

Secondly, assuming that you are talking about NEET. Then, in case of a payment lapse, you can simply  again by entering your registration number and password in Candidate Login area. The portal will show that your payment is pending and you can initiate the payment again.

Remember that the generation of a final confirmation page after the payment will indicate a successful submission of NEET application form. You can check all complete step by step guide and video guide of filling NEET application form from the link given below. I hope it will resolve all your queries. 

Guide on filling NEET 2018 Application Form

Hope it helps! All the best!