Hii Manish!

This may have happened because of poor network connection or too much traffic on the website. This problem is usually soughted out within 24 hours or else, if it doesn't get solved, you can call on the helpdesk for neet and enquire about the same. If we talk of payment receipt, it is not required on the exam day to enter the centre. You get an entry with your admit card and valid ID proof on the centre. So you don't need to worry about that. But yes, do get this receipt problem solved by contacting the helpdesk. Hope this helps.

Good luck!