UPI apps not opening from Iphone browser but its working on Android

<a href="upi://pay?pa=UPIID@oksbi&amp;pn=FNAME SNAME K&amp;cu=INR" class="upi-pay1">Pay Now !</a>

When we use the above code the apps like GooglePay, PhonePe, Whatsapp, Paytm working in Android, but same url opens always whatsapp in Iphone