The error is due to the fact that eBay is detecting insecure code (HTTP and not HTTPS) between the HTML links in your template.

First, make sure that your e-commerce is using secure mode (SSL) and has a valid certificate installed.

If you are using a custom eBay template, carefully check the source code and make sure it does not contain links or links to images, pages or CSS in HTTP format.

If you have Prestashop descriptions that contain links or HTML elements in addition to text, check the source code of the description and make sure that they are exclusively in HTTPS and not HTTP. If not, change them to HTTPS.

If you have updated the module from a previous version and you are using the old {GALLERY_V} tag to show product images dynamically,
you must remove it from the template as it is no longer supported by the new eBay rules.