Yeah, this complicates things 
In most cases, we are unable to effectively troubleshoot outdated libraries, especially if the difference goes beyond minor updates within the same major version. So this would be the first step I’d ask you to take when you can.
If possible, please try spinning off this Quickstart and use it with your tenant:
It’s also worth a shot to try using /delegation in Postman/Insomnia to see if it works with your tenant: