Tattoo Smart's brush downloads only work using the Safari browser.
If you are using an alternate browser, such as Google Chrome, please close your browser and launch Safari. Additionally, please do not use a private browsing window.
Then follow the steps in the installation video that was included with your order.
These steps can also help:
Update Procreate and your iPad OS software in the App Store - if you do not, your iPad/Procreate will not recognize the .brushset file type.
Clearing the cache on Safari: http://www.macworld.co.uk/how-to/iphone/how-clear-cache-on-your-iphone-or-ipad-3609079/
Allowing cookies: https://support.apple.com/en-us/HT201265
Allowing enough time to download: the new Procreate .brushset files are very large so make sure you’re using the strongest internet connection you have access to.
If those steps do not work, Just email firstname.lastname@example.org and include your name, order number, and a brief description of the problem.