Concatenation bug in php8

We found a bug when upgrading from PHP 7 to PHP 8.

The bug is on woo-vipps\WC_Gateway_Vipps.class.php:1684
$msg = $msg + __(" - order does not need processing", 'woo-vipps');

The plus operator is used for concatenating strings, it should be a period.

PHP 8 is stricter about this and caused our site to crash. Everything worked fine when we change the plus to a period.

Please fix this ??