A version of PHP that is compatible with WishList Member needs to be installed and running on the server. WishList Member requires PHP 5.6+ (PHP 7.4+ recommended) in order be installed and function correctly in the hosting environment.
If your server/hosting provider is running an older version of PHP then errors can occur when trying to upload or update WishList Member.
You can contact your server/hosting provider to determine if PHP 5.6+ (PHP 7.4+ recommended) is running. If it is not, it should be a quick process for your server/hosting company to upgrade accordingly.