Parse error: syntax error, unexpected ‘:’, expecting ‘{‘ in . Error when require_once autoload.php

I have problem when trying to connect to google api php client. Although this version was introduced for use with php 5.6 and above, it is actually not true of the structure of php5.6. My php version is 5.6

This is a function that autoload.php runs through when i require_once autoload.php

function default_ca_bundle(): string
{
    return Utils::defaultCaBundle();
}

Answer

This is function return type declartion. This feature introduced since PHP 7.0, so it can not be used in PHP 5.x

Here you can test code with different PHP versions