Add a 'where will you be promoting ___' to AffiliateWP's registration form

gistfile1.php

<?php

// add a 'where will you be promoting ___' to AffiliateWP's registration form
add_action( 'affwp_register_fields_before_tos', function() {
	?>
		<p>
			<label for="affwp-user-where">Where will you be promoting SearchWP? USE SPECIFIC URLs (e.g. websites, social networks, etc.)</label>
			<textarea id="affwp-user-where" name="affwp-user-where"></textarea>
		</p>
	<?php
});

add_filter( 'affwp_registration_email', function( $message, $args ){
	if ( ! empty( $_POST['affwp-user-where'] ) ) {
		$message .= "<br /><br />Where: " . esc_html( $_POST['affwp-user-where'] );
	}
	$message = str_replace( "\n", '<br />', strip_tags( $message ) );
	return $message;
}, 10, 2 );

add_action( 'affwp_process_register_form', function() {
	if ( ! isset( $_POST['affwp-user-where'] ) || empty( trim( $_POST['affwp-user-where'] ) ) ) {
		affiliate_wp()->register->add_error( 'where', 'You must indicate where you will be promoting SearchWP' );
	}
});