Web filtering with URL filtering only and BYOD

Hello,

I have a question about the configuration of my UTM. At the moment here is the situation :

• I have a UTM with FQDN
• I have two types of computers in my network :
  
  • Computers who can have UTM certificate
  • BYOD in which i cannot ad the certificate

Here are screenshots of what appens when computers try to reach a forbidden website

Computer with UTM certificate :

Computers BYOD without UTM certificate :

Its good for me but i would prefer to have the best display for my Sophos warning for BYOD

Following this thread : https://community.sophos.com/products/unified-threat-management/f/55/t/47035 here is what i've done :

1. Create a new certificate passthrough.srv.domain.com
2. Upload the certificate in :  Webserver Protection > Certificate Management > New certificate
3. Select the certificate in : Webprotection > Filtering option > Misc
   
   1. Activate "Use a custom certificate for HTTS pages"
   2. Hostname : passthrough.srv.domain.com
   3. Select certificate for passthrough.srv.domain.com

Here are screenshots of what appens when computers try to reach a forbidden website

Computer with UTM certificate :

Computers BYOD without UTM certificate :

Does anyone have an idea ?