If you are seeing something similar to the image below, where your browser is informing you that www.myp11d.com is 'Not Secure', then you are having issues with authenticating the SSL certificate.
The SSL certificate that is applied to a web site is issued by an authorising body - when a server looks at an SSL certificate is picks up some information and then contacts the authorising body to check that the certificate is authentic. All subscriber certificates are issued by an Intermediate Certificate - these Intermediate Certificates are issued by a Trusted Root Certificate.
The Issuer may vary depending upon the type of certificate and we send Intermediate Certificates with the subscriber certificate. Therefore. to make contact, the web browser needs to be able to communicate to the authority in question - in our case it is a company called Sectigo that provides the RSA Validation - therefore communications to their site is crucial.
Resolving the issue
You will need to get your IT team to ensure that crt.sectigo.com is allowed through the firewall/proxy. Once allowed, your browser will no longer show the site as insecure:
You can verify the authority by clicking on the padlock and viewing the certificate information (see below)