Check how to resolve “Order was not created. Reason: This product is currently out of stock" error. 

Read what to do if "Mage registry key already exists" error occurred after the Module installation/upgrade.  

Check how to resolve "Order was not created. Reason: Please specify a shipping method" error.

Learn how to resolve “The listing was locked by another process. Please try again later”  error.

The errors may occur during the Subscription activation process if the data (value) has been cached.