users.settings.delegates List not showing delegates and Create not adding Groups

I've created a flow which creates a JWT token from a service account impersonating the mailbox account, it creates a Google Group based on some of the property names. Another JWT Token is created impersonating a bot account that has Group Admin role, this is to patch the group to hide from Address List (avoid people emailing it). The issues encountered are as following:

- When creating the Google Group, all is well, but when adding it as a delegate to the mailbox it keeps giving error saying "Invalid Delegate" however the delegate does exist in Google Admin and does work if manually done from the Mailboxes Account Settings.
- When trying to get details on extra parameters, I attempted a List delegate on the mailbox and keep getting a 204 response with the body being ""
Appreciate the help on this one 🙏

Start by reproducing the users.settings.delegates List and Create calls using the JWT impersonation flow described in the issue, recording the 204 response and Invalid Delegate error. Compare those results with manually adding the delegate in the mailbox settings and verify whether the client request or the upstream Google API is responsible; done means identifying a reproducible fix or a documented upstream limitation.

索引モデルが issue の本文から書いたものです。