What It Means
A UPI Mandate is the approval request your bank sends to your UPI app when you apply for an IPO through your broker or bank. Approving it doesn't pay for anything right away. It just lets your bank block, or reserve, your application amount inside your own account so it can't be spent elsewhere.
How It Works
Your money never leaves your account at the application stage. It stays put, still earns interest, and simply gets marked as reserved once you approve the mandate. If you're allotted shares, the bank debits only the amount for the shares you actually received. If you're not allotted anything, or you're allotted fewer shares than you applied for, the rest of the blocked amount is released automatically, with no action needed from you.
The mandate request usually has a short approval window, often just a few hours. Miss it, and your application can get rejected outright even though you filled out the form correctly, because the bank never received authorization to block the funds.
Warning
The most common way people accidentally miss out isn't a mistake in the application form. It's forgetting to open their UPI app and approve the mandate in time, which gets the whole application rejected before it even reaches the draw.