PrestaShop displays that the module is not verified during the installation
Since one of the latest versions of PrestaShop, this message appears when you try to install a version that does not originate from PrestaShop Add-ons.
PrestaShop attempts to redirect you to a paid version but the module that you have downloaded is, in fact, the official version of Systempay and is perfectly compatible with PrestaShop.
You can safely proceed and click on Continue the installation.