Curly brace syntax for accessing array elements and string offsets has been deprecated in PHP 7.4: https://wiki.php.net/rfc/deprecate_curly_braces_array_access
$hash2{$i} should be $hash2[$i]
PHP Deprecated: Array and string offset access syntax with curly braces is deprecated in ./vendor/mediawiki/oauthclient/src/Client.php on line 414