WordPress gives the error “invalid plugin” when I try to install the PayFast module.

Our plugin is not a plugin for WordPress itself, but for EventEspresso, which is itself an ecommerce plugin for WordPress.

To integrate with PayFast, you will need to install EventEspresso first. Once you have installed WP e-Commerce, you can then install the PayFast payment module for WP e-Commerce provided by PayFast, as detailed here.