I was able to solve the same problem! Simply to your VirtualMin > Select the domain > Server Configuration > SSL Certificates. If you have already installed your certificate file (.crt) and private key (.key) then you will need to “CA Certificate” to upload your intermediate certificate file. I recommend to update the file to avoid copy errors as ssl files are very sensitive to change.
Once this is done, go to “Update certificate and key” tab to re-upload your cert file, for the key you can use “keep existing private key” if you have uploaded before it before.
You can restart apache after then. I hope this helps!