Check the exact URL you are using in the GlobalProtect client. If your IT department gave you gp.mycompany.com , ensure you didn't type gp.my-company.com . A single character mismatch triggers the error.
By 3:15 AM, the coffee was cold, but the logs finally turned green. Marcus had manually pushed the full certificate chain to the Palo Alto gateway and cleared the local cache. globalprotect vpn failed to verify certificate