Dynamically populate email field value

Thank you for the direction! I was able to create a smart tag that allows adding email from http $_POST.

NOTE: It also supports query var if you are already linking your form page using query var and email (you should not!).

Here is the code if anyone interested!

/**
 * Register the Smart Tag so it will be available to select in the form builder.
 *
 * @link   https://wpforms.com/developers/how-to-create-a-custom-smart-tag/
 *
 */
function aud_http_request_email( $tags ) {
 
    // Key is the tag, item is the tag name.
    $tags['http_request_email'] = '$_REQUEST Email';
 
    return $tags;
}
add_filter( 'wpforms_smart_tags', 'aud_http_request_email' );
 
/**
 * Process the Smart Tag.
 *
 * @link   https://wpforms.com/developers/how-to-create-a-custom-smart-tag/
 *
 */
function aud_http_request_email_smart_tag_process( $content, $tag ) {
 
    // Only run if it is our desired tag.
    if ( 'http_request_email' === $tag ) {
		
		if( isset( $_REQUEST['email'] ) && is_email( $_REQUEST['email'] ) ){
			// Replace the tag email
			return sanitize_email( $_REQUEST['email'] );	
		}
		
		// replace tag with empty string
		return '';
    }
 
    return $content;
}
add_filter( 'wpforms_smart_tag_process', 'aud_http_request_email_smart_tag_process', 10, 2 );

# How to use this code?
You can use https://wordpress.org/plugins/code-snippets/ plugin to add this code into your site. Or you can paste the php into your themes functions.php file.