Your UPI mandate may fail sometimes despite receiving the IPO allotment, due to technical issues from your bank’s end. 

Your funds are debited from your account based on an allotment file which the registrar shares with the banks. In case of any technical issues, the bank will re-attempt to debit the funds. The responsibility lies with the bank to ensure that the funds are debited from your bank account and given to the issuer’s bank.

The shares will be credited to your demat account and will be available for selling on the listing date even if your funds aren't debited.