Error 0 [] operator not supported for strings

Hi, when changing server php from 7.0 to 7.1 I get this error message on my site:

Error 0
[] operator not supported for strings
It appears the page you were looking for doesn't exist. Sorry about that.

Latest Template version + J3.8.12
Works fine with PHP 7.0 or 6.5.

Thanks

Hi,

Please update your template to latest version (3.23), you are using 3.22 now..

Cheers
Joshua