Plugin fails on final step

[guycalledseven]

When using plugin with newer sylius (tested on v1.8.1.), final step of payment (redirection to payway) fails with error:

Argument 1 passed to Payum\Core\Gateway::addAction() must implement interface Payum\Core\Action\ActionInterface, string given, called in /var/www/vendor/payum/payum/src/Payum/Core/CoreGatewayFactory.php on line 219

dev.log shows this critical error:

[2020-10-06 15:07:48] php.CRITICAL: Argument 1 passed to Payum\Core\Gateway::addAction() must implement interface Payum\Core\Action\ActionInterface, string given, called in /var/www/vendor/payum/payum/src/Payum/Core/CoreGatewayFactory.php on line 219 {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalThrowableError(code: 0): Argument 1 passed to Payum\\Core\\Gateway::addAction() must implement interface Payum\\Core\\Action\\ActionInterface, string given, called in /var/www/vendor/payum/payum/src/Payum/Core/CoreGatewayFactory.php on line 219 at /var/www/vendor/payum/payum/src/Payum/Core/Gateway.php:66)"} []