Pay Now Button with upi:// Link in HTML Email is Not Clickable

I'm creating an HTML email template with a "Pay Now" button that links to a UPI payment URL. Here's the code for the button:

<a href="upi://pay?pa=example@oksbi&pn=John%20Doe&tr=%20&am=500&cu=INR" target="_blank">Pay Now</a>

The button is styled and renders properly. However, the link is not clickable in Gmail, and it doesn't open the UPI payment app when clicked.

Interestingly, when I share the same link over WhatsApp, it works perfectly and opens the UPI payment app as expected.

Any work around for this issue?