Sorry to see you are experiencing a problem with the theme.
We are not getting this error on any of our test sites or our demo.
So that I can investigate this further, could you let me know the version of PHP that your server is running?
If you have WooCommerce installed, go to ‘WooCommerce’ > ‘Status’ and under the ‘Server environment’ heading it will say PHP version:
If you are not using WooCommerce, could you install the Debug Info plugin, then look in ‘Dashboard’ > ‘Debug Info’ where it will show which version of PHP you have.