You are allowed to use the template for your clients, as long as you do not RESELL it as your own. It is a template you can alter to suit the needs of your end product.
Yes, you need an account with ManyChat before being able to use these templates
Unfortunately, most emails end up in spamfolders these days. If you use a free email service provider, this is even more so. Please check your spam folder/unwanted email folder to see if our email is in there. The sender of the email is email@example.com
Once you have paid for the template you desire, you will see you download in your account in the Purchase History. Also, you will get an email confirmation with your download link.
You can click the link to the chatflow, which will take it into your own account at ManyChat (you need an account with ManyChat before being able to use these templates). Once in your own ManyChat account, you can clone the flow and edit it to your liking.