Sendybay automatically applies SSL certificate for your custom domain. You don't have to set it up yourself.
Chrome might be warning you that website is not secure. Here's how it looks like -
In this case, the likely scenario is you are facing cache issue. Try verifying the SSL using a third party service like SSLShopper.com or try loading the website in Incognito.
If you are still seeing this error message, reach out to our support team at support@sendybay.com