protected function get_order_id() {

		$order_id = null;
		$key      = $this->data['llms_order_key'] ?? null;
		$email    = $this->data['email_address'] ?? null;
		$plan_id  = $this->data['llms_plan_id'] ?? null;

		// Try to lookup using the order key if it was supplied.
		if ( $key ) {
			$order_id = $this->sanitize_retrieved_order_id( llms_get_order_by_key( $key, 'id' ) );
		}

		// Try to lookup by user ID.
		if ( ! $order_id ) {

			$user_id  = $this->find_user_id( $email );
			$order_id = $user_id ? $this->sanitize_retrieved_order_id( llms_locate_order_for_user_and_plan( $user_id, $plan_id ) ) : null;

		}

		// Lookup by email address.
		if ( ! $order_id && $email ) {
			$order_id = $this->sanitize_retrieved_order_id( llms_locate_order_for_email_and_plan( $email, $plan_id ) );
		}

		return $order_id ? $order_id : 'new';

	}