If the domain name you want to use is already attached to another Alibaba Mail instance, you can complete the purchase with a different domain name and then change it in the console.
Problem
When you purchase an Alibaba Mail subscription and enter your domain name, the following error message appears: The domain name you entered is already attached. Use a domain name that is not attached. This error occurs because the domain name is already bound to another Alibaba Mail instance.
Solution
Follow the prompt to enter a different available domain name and complete the purchase.