Change user role for buyers

function ao_edd_set_customer_role( $payment_id ) {

	$email     = edd_get_payment_user_email( $payment_id );

	$downloads = edd_get_payment_meta_downloads( $payment_id );

	$user_id   = edd_get_payment_user_id( $payment_id );

	if( $user_id ) {

		$user = new WP_User( $user_id );

		// Add role

		$user->add_role( 'buyer' );

	}

}

add_action( 'edd_complete_purchase', 'ao_edd_set_customer_role', 100 );