Thank you for getting back to us. What is happening here is that not all the content on your site is being loaded through the HTTPS protocol and this is why you are receiving this error about attackers being able to see the images.
When you try to upload your own SSL certificate you mentioned that you are getting an error message, what is that exact error?
Additionally, Ezoic does indeed provide you with an SSL certificate, would it be better to use the Ezoic one and disable the IONOS SSL, this would be a more compatible set up with Ezoic?
I look forward to hearing from you soon.