Hi LeoLeon___ ,
It seems like your site might be using PHP version 5.
Could you confirm if this is true?
Since the release of Buttonizer 2.1, we have optimized Buttonizer using PHP 7 features and no longer support PHP version 5.
If you are still on PHP version 5 or lower, we recommend that you upgrade to the latest version.
We have made an article in our knowledge base about why and how you should upgrade to PHP 7.
PHP version is outdated
Please let us know if this was the case!