Warning with PHP 8.1.26

Hello. Using the plugin in an environment with PHP 8.1.26 we get the following warnings:

Warning: Undefined array key -1 in […]/wp-content/plugins/scalapay-easy-installment-gateway/scalapay-easy-installment-gateway.php on line 325

Warning: Trying to access array offset on value of type null in […]/wp-content/plugins/scalapay-easy-installment-gateway/scalapay-easy-installment-gateway.php on line 325