Declaring an iframe

Create an HTML <iframe> tag on the page where you would like to display the payment page (this page should correspond to the "Payment" stage of your purchase journey).
Use the name attribute to give a name to your iframe. This name will be used in the payment form to specify within which item the form will be displayed.
Populate the src attribute with your payment form URL.
Define the size of the iframe by using the width and height attributes.
Use the scrolling attribute of the iframe tag to delete borders and scrollbars.

Example:

<iframe name="nameFrame" src="payment_form.php"    scrolling="no" />