This is possible due to various reasons, for instance,
1. OTP was not received/ delayed
2. Ongoing Bank’s downtime which is not allowing a transaction to go through
3. Customer changed his mind
4. Slow/flaky internet at customer’s end
5. Customer closed the 3D secure page during transaction
6. Customer didn’t confirm the payment in his/her UPI mobile app etc.
Please try again and wait for the transaction to be completed.