Thanks for the question, and welcome to Apple Support Communities.
The following article provides an answer to your question:
Downloading a pre-ordered item
When a pre-order item becomes available, you will receive an email letting you know your pre-order is available for download.
If you've enabled iTunes to automatically download prepurchased content, then your pre-order content may already be downloaded to your library. If not, simply click the download link provided within your email notification, and your pre-order content will begin to download. Alternatively you can use the "Check for Available Downloads" feature in iTunes on your computer by choosing Store > Check for Available Downloads to begin downloading your pre-order.
I'm having the exact same problem as many people I suppose. Pre-ordered an album, received an email saying it was now available to download, please click on the link. No luck. I preordered it on my phone using iTunes and every other album, movie, app have downloaded straight away even when it's been preordered. I have followed the advise on the forum. For example sign out and sign back in. Click on downloads etc, but mine just keeps coming up as no available downloads and the album is only showing up as purchased. Waiting 4 months for an album, having paid for it and then finding out it won't work is completely gutting. Please help! :( p.s I don't have access to a PC/laptop. All is done through my phone
I'm having the exact same issue as the original poster except I did everything through my Desktop PC. It shows as purchased when I login to the iTunes. I got the original 4 songs that were available early, but now I can't get the rest of the album. I have it set to automatically download content from preorders when available, it just isn't doing anything. No matter what I try, it will not come over. I'm probably never going to preorder again since I see this appears to be a common issue.