Parse error: syntax error, unexpected 'const' (T_CONST), expecting variable (T_VARIABLE) in /[path_of_install]/wp-content/plugins/woocommerce-izettle/autoload.php on line 58

If you get this error message it means your php version does not meet the requirements of php 7.1. Please ask your hosting partner to upgrade your server to meet this requirement.

In case you want to push your hosting partner into the right direction, send them this link which shows the officially supported versions and their end-of-life:
http://php.net/supported-versions.php