This error message means that there is an issue with your PHP version. Please make sure to use at least the minimum required PHP version or higher. You can verify the PHP version of your WooCommerce installation under WooCommerce > Status > System Status > Server environment.
You can check the minimum required PHP version at https://wordpress.org/plugins/cryptocurrency-payment-gateway/.
Please note: In some cases, this error is triggered during the execution of the cron job. The PHP version used in a server cron job can be different from the PHP version used by your web server. Please make sure your server cron job uses a compatible PHP version, or use the alternative cron job command that starts with "wget" instead of the default command.
Did that not fix the issue?
Contact us at https://cryptowoo.zendesk.com/hc/en-us/requests/new, and please include the full error message in your request.