How to add external contacts to google shared address book?

Question

Google

Gentlemen, this is the thing:
There is a business mail for a domain, inside which there are a bunch of accounts registered.
They all use an internal address book, which is essentially a list of domain users.
There is a great keen desire to cram other addresses outside the domain into these common contacts.
Here in tyrnets they write that there is a special API, there are even third-party services, but I'm stupid, probably, I didn't understand anything anyway.
I even added www.apptivo.com, but still, for some reason, my personal contacts are not shared with everyone else.
Yes, I know that I can share access to my address book to other employees using Google, but this must be done with each user separately, and you cannot share it with a group.
Colleagues, maybe you have already solved similar problems somehow?
How to write external mailboxes to Google's shared address book for a domain?

Answer 1

except to create groups and
add an external user soap in the Advanced group settings