Transferring music between devices
Hi,
I just bought an album on iTunes on my iPad, how do I get this album on my iPhone, it's the same apple ID
You might be able to re-download it on iPhone via the Purchased tab in the iTunes store app on it : re-downloading.
If you aren't in a country where music can currently be re-downloaded then you will need to connect the phone to your computer's iTunes and copy it over via File > Transfer Purchases (File > Devices > Transfer Purchases), and you then sync it to your iPad.