When in the shop, if you click on a button to purchase and a loading wheel comes up, but nothing else happens, then it may be that your in-game overlay is disabled. Currently purchases can only be made if it is enabled.
To enable the overlay:
- In steam, select the Steam from the top menu bar, and go to Settings.
- Select the In-Game tab.
- Check to make sure "Enable the Steam Overlay while in-game" is selected
If you are still unable to initiate a purchase, you can create a support ticket. Please let us know your hero name and any error messages you are receiving.