Sadly, it is simply a poorly created "web embed" implementation and will require going back and forth between wix and charm but eventually it does work (but even then will still be poorly mobile responsive). Most platforms create a defined scheduling landing page that you would simply link a button on your website to and would then be far easier and responsive but not the case for Charm despite much feedback.
from your screen shot, I am not seeing that you added the url that the error message provided to your "hosting websites" area.
to do this, edit your existing web embed in charm by clicking the "..." next to it.
then enter the link that the error message provided beneath your existing clinic url and save.
then take this regenerated code and copy that into your wix html box and refresh. it may likely give you another error message with a new url to add. repeat this step as many times as needed and it will generally work in time.
a pain for sure and far more complicated than simply linking a charm generated scheduling landing page such as: