Trial expired before it started

I have just downloaded the Audirvana app on my MacPro running OS X 10.11.6.
It is telling me ‘The trial period has expired. Please enter a purchased license key to continue using Audirvana.’
Yet I have received an email welcoming me to a free 30-day trial. What can I do to continue getting started with the app on my Mac?
I have never tried Audirvana before.