Your server is presumably running a version that’s older than that, so you’d have to look at upgrading or switching the PHP version, or switching servers.
Thank you for your feedback.
I configured PHP 7.1 version and now the home page with the default theme is ok, but accessing to the site https://abruzzocultura.com/omeka-s/s/MuNdA I have the following error:
Omeka S encountered an error
Exception
The current theme is not active. Its current state is “invalid_omeka_version”.
Details:
Exception: The current theme is not active. Its current state is “invalid_omeka_version”. in /home/touristr/public_html/abruzzocultura.com/omeka-s/application/src/Mvc/MvcListeners.php:328 Stack trace: #0 /home/touristr/public_html/abruzzocultura.com/omeka-s/vendor/zendframework/zend-eventmanager/src/EventManager.php(322): Omeka\Mvc\MvcListeners->preparePublicSite(Object(Zend\Mvc\MvcEvent)) #1 /home/touristr/public_html/abruzzocultura.com/omeka-s/vendor/zendframework/zend-eventmanager/src/EventManager.php(179): Zend\EventManager\EventManager->triggerListeners(Object(Zend\Mvc\MvcEvent), Object(Closure)) #2 /home/touristr/public_html/abruzzocultura.com/omeka-s/vendor/zendframework/zend-mvc/src/Application.php(311): Zend\EventManager\EventManager->triggerEventUntil(Object(Closure), Object(Zend\Mvc\MvcEvent)) #3 /home/touristr/public_html/abruzzocultura.com/omeka-s/index.php(21): Zend\Mvc\Application->run() #4 {main}