You would face the root certificate not trusted error is the Securly SSL certificate is not installed on your Mac OSX.
To stop receiving the error you would, therefore, need to install the SSL certificate.
- Download the Securly certificate CRT file.(Link)
- Navigate to Finder > Applications > Utilities > Keychain Access
- Select ‘System’ in the left-hand column.
- Open ‘File > Import Items’ and import the ‘securly_SHA-256.crt’ files into the ‘System’ keychain.
- Alternatively, you can automate the installation process via MDM by downloading the ‘OSX SSL Install Securly.zip’ file at the end of this article. The file contains a .app that would automate the process. There is also a .tar file that can be used directly on a Mac.