Apologies for the delayed response. Please be aware that you can file a support ticket at any time from under the Help tab of the site with questions, concerns or issues you run into and our support team will be happy to assist you.
You would not be able to effectively post any listings that still have HTTPS content from templates as eBay no longer allows any such content on listings. If you are using the standard image selection tool for images in your listings you would not need to be concerned with making changes to the images as we store all images as HTTPS, as we have since this became relevant for browsers and eBay. However, if you have older listings where you inserted images directly into the HTML or used the Insert an Auctiva Hosted Image tool in the description editor, you would need to make the changes to those images as our tools would not update those and they would likely have the HTTP format that was in common use at that time.
There are a variety of bulk tools that are also available that may help you with your older saved listings, depending on their state at this time; these are available under the Advanced Edit tool on the Saved Listings page - there are bulk tools to assist with changing the template on listings as well as active content (although the HTTP to HTTPS issue is not active content).
If you run into difficulty, please feel free to file a support case and our team will be happy to assist you further.