If you can't click the process button, it probably means you are on our free account. Since free users are only allowed to process 10 second previews, you'll have to click 'preview' instead.
If you'd like to switch to a pro account, you'll have to add your payment details by going to Settings > Billing from your dashboard.
Please note that pro users are charged for storage, downloads and processing. If you want to go back to being a free user, simply settle all outstanding balances and delete your payment details.
More information can be found on our pricing page.