Wordpress Shortcode for embedding form with prefilled fields

functions.php

<?php

// [airtableform form_id="shr1St9pPOAptb7r8"]
function airtableform_func( $atts ) {

	$a = shortcode_atts( array(
		'form_id' => '',
		'width' => '100%',
		'height' => '533',
		'color' => 'red',
	), $atts );

	$current_user = wp_get_current_user();

	$prefill_string = "";

	if ( $current_user->exists() ) {

		$prefill = [
			"Name" => $current_user->user_login,
			"Notes" => $current_user->user_email
		];

		foreach($prefill as $key => $value){
			$prefill_string .= "&prefill_" . rawurlencode($key) . "=" . rawurlencode($value);
		}

	}

	return '<iframe class="airtable-embed" src="https://airtable.com/embed/' . $a["form_id"] . '?backgroundColor=' . $a["color"] . $prefill_string . '" frameborder="0" onmousewheel="" width="' . $a["width"] . '" height="' . $a["height"] . '" style="background: transparent; border: 1px solid #ccc;"></iframe>';

}

add_shortcode( 'airtableform', 'airtableform_func' );