A problem often encountered after installing a Pretashop application is the "white page" when accessing the admin domain.tld/administrator address (the address may be different depending on the customizations made when installing the application).
Generally the cause of this error is due to the fact that PHP directives opcache.save_comments and opcache.load_comments are not activated.
This error can be seen in the file error_log from the directory where the administration part is loaded. An extract from the error log would look like this: PHP Fatal error: Uncaught exception 'Doctrine\ Common\ Annotations\ AnnotationException' with message 'You have to enable opcache.save_comments=1 or zend_optimizerplus.save_comments=1.' in /home/XXX/ public_html/ PrestaShop/vendor/ doctrine/annotations/lib/ Doctrine/Common/ Annotations/ AnnotationException.php:183
To activate these two directives we will access cPanel -> Select PHP version -> Switch to PHP Options and we'll put the two directives on On, after which we will click on the Save button at the bottom of the page.
More details about modifying PHP directives can be found in the tutorials:
For shared spaces: Directive PHP Shared
For VPS spaces with cPanel: Directive PHP VPS
After setting these directives to On , the admin side should become accessible.