Hi:
It’s probably for the best ! 
There are currently issues with the Spring sale… players who bought games can’t install them… there is a workaround, but it doesn’t seem to work for all… see:
The sale ends on May 7… give it a few days and try again. Perhaps Blizzard will figure out what the issue is and be able to fix it…
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Also… you should be posting on the Diablo IV forums: