Log in to HDFC NetBanking or the HDFC MobileBanking app
Go to Cards or Debit Card Services
Select your debit card
Choose Manage Usage or Card Controls
Enable Online Transactions or E-commerce Transactions
Set the transaction limit if required
Save or confirm the changes
Alternatively, use an HDFC ATM and select Debit Card Services to enable online usage
If needed, call HDFC customer care or visit the nearest branch for assistance