I got this myself on my iPhone, and it was very frustrating. I tried downloading a song but it kept coming up download error. Tap to retry.

I could retry forever, it wouldn’t work.

However, I did notice that before it actually went and failed, there was a pause button available for about .5 seconds. If you can hit that pause button before the download quickly fails, it will then restart. The download should work as normal after unpausing it.

Let me know if you have any questions.