Hi,
Acymailing v8 has a new, user-friendly drag & drop editor that makes creating templates and emails easy. All you need to do is drag a structure block into your mail and then drag the type of content block you want into the structure block. For more information on how to use the drag & drop editor, please refer to the documentation here: https://docs.acymailing.com/main-pages/templates/create-a-template
Alternatively, you can use the CMS editor to work with HTML templates. When you create a new template, you will be given the option to choose between a HTML template and the drag & drop editor. Once you have created the template, you can use it to create your mail and the CMS editor will appear instead. Please note that Acymailing is focusing more on the drag & drop editor and you may miss out on some features if you opt for the CMS editor.
If you have encountered any changes with a group during the migration process, please submit a support ticket here: https://www.acymailing.com/support/ so that we can provide more assistance. We will also be able to investigate why you are unable to send a test mail.