If you received one of these errors, you've probably provided an HTTPS-based image URL. Walmart Product Content Policy recommends using an HTTP URL for images.
As a solution, you can navigate Walmart > Configuration > General > Advanced (M2E Pro v6.5.5 and higher for Magento v1.x) or Walmart > Configuration > Settings > Main Tab > Advanced section (Magento v2.x) and configure automatic URL replacement. Choose Replace with HTTP option and click Save. After this, all image URLs will be automatically replaced to HTTP-based URLs.
If you’ve configured the settings and the error still appears, please make sure to turn off the HTTPS URL redirect on your web server.