Welcome to AbanteCart Danny,
This is not an error and works as warning. Also, this is not a coding issue.
Warning basically indicates that somebody or something accessed your AbanteCart site with incorrect (not configured) domain/URL.
It mainly indicates that your site can be accessible with different domains or subdomains that indicates misconfiguration on your web server.
This is not about HTTP to HTTPS.
Common example that will trigger this warning is, then your AbanteCart can be reached by
www.xyz.com and xyz.com without automatic redirect of xyz.com to
www.xyz.com.
In this case, you need to set a correct redirect to
www.xyz.com within web server or .htaccess configuration.
In event you need to use multiple domains in one AbanteCart, you can use multi-store configuration.
Also, this warning lets you know that there is a potential search engines issue. If search engines see your site in different domains, they give you penalty.
Hope this helps to clarify the situation.