From where can I get a domain id for a specific domain in an instance?
You can find the ID of the domain you’re currently in, via the response of the
/me endpoint (you must be logged in to receive this information):
It also contains IDs for all Domains your user is registered in.
To be specific @Flogge the endpoint is called
Alternatively, you could use
/domains, but it has the same restrictions - it only returns domains the user has access to.