The download links found in your invoice email will only last for a certain time before they expire.
Once expired you will not be able to use these links to download the plugin/s again.
Instead, you can access the latest version of your plugins at any time by logging into your account.
Login to your account by clicking the Login link in the top menu of our site.
Once logged in you will see a section called Downloads which contains all the products you have access to along with your license information.
These links will always point towards the latest version of the product.