There is no way that we can have a URL for ServiceNow certification. However, one way is to upload your certificate to Google drive or any other drive and grant public URL access to it and use this URL in the Linkedin certification URL Field so that anyone who clicks it can see your cert.
Please see if you can mask the certification ID in that PDF as most scammers are known to misuse the ID for personal gains and reduce the importance of your had earned cert. Thanks !
