we've encountered error in subject of this post continued by:
"0 - A certificate chain could not be built to a trusted root authority.
ISSUER: CN=GlobalSign RSA OV SSL CA 2018, O=GlobalSign nv-sa, C=BE
This warning can be disabled by clicking Tools -> Options."
This seems to be problem with local certificate store on client computer? Not neccessarily Fiddler issue.
Using Windows 7.
How do we proceed?
Is the issue happening with the latest version of Fiddler Everywhere (1.6.1 and above)?
You can share your network configuration (is there a VPN tool, additional security tooling or any kind of anti-MITM software or other MITM software that might be working on your client's station).